AP over A Races not started are postponed. No more racing today.

If the race committee has decided that the last two races will not be sailed the races are abandoned and the signal is N over A.

That is a good point. The RRS define "postpone" and "abandon" but they do not define "no more races for this regatta". It seems logical to use AP over A, because that is typical but it really doesn't say that all potential races will not be sailed.  The RRS definition for "abandon" allows that the races may be sailed at a later date. 

Normally N over A indicates end of racing for a regatta/series. N indicates - all other races are abandoned, in this case 2 races left of 8. A indicates today. AP over A (or H) indicates that races not taking place are postponed - i.e. will be sailed at a later date. N over H is also commonly used.

It would stand to reason, if the NOR has a time limit, that N over A flown on the last day of the regatta with a time limit for the day would send the message that there are no more races at all, not just for the day.

If you want to send boats home as they finish, AP over A is the appropriate signal. N over A indicates that All races are abandoned. No more races today. So N over A should not be displayed until after the last boat has finished the last race sailed (in the example give by Thomas, race 6).

As an aside, N signals that "All races that have started are abandoned .........." so I suggest that there is some potential for confusion/requests for hearing, by displaying N over A while any boat is still racing.

You should use N over A if a race has started. And AP over A if a race has not started yet. In the NOR and SI the dates for racing are specified. If on the last day are race is postponed under AP over A or abandoned under N over A the event is closed. Because there are no more racing days. 

Typically AP over A is used which indicated that all races not started are postponed and no more racing today.  So if it is the last day of the regatta then the time limit will expire.  If there are further days in the regatta then AP over A or N over A should be used on any subsequent days until the last day of the regatta and the time limit expires.
Note that if you use N over A then any race that is in play is being abandoned.
Also if you use AP over H or N over H then you will need further signals ashore.

recommend the US Sailing prescription: US Sailing prescribes that, if the sailing instructions so state, the race committee may display flag A (with no sound) while boats are finishing to signal that there will be no more races conducted that day. 
Makes it clean and reduces the thinking 

Since I started writing this, others have opined along the same lines.

We've had this discussion in another thread somewhere. Since then I've done a bit of digging and found the WS Race Management Policies for Fleet Racing. The section on Abandonment has 7 items, none of which consider abandoning a race not started. The section on Postponements only considers postponing during the starting procedure, which I infer applies to any time prior to the actual or scheduled start of a race.

If the regatta is scheduled to end on such and such a date, it's ended then unless there is a provision to reschedule. Since I prefer to keep things simple (the KISS concept) and distinct, and since the different terms are defined, abandonment applies to races actually started, and can apply to a race even after one or all have finished for all kinds of reasons. Races not started are postponed (although may be sailed later, if there's time in the schedule). If the postponement is on the stated last day of the event, the calendar supersedes the possibility of sailing them another day.

This mitigates any confusion inherent in the definition of N over A, which contains two statements - that 1) ALL races are abandoned. and 2) No more racing today. The question of which races are abandoned (statement 1) is not signaled or defined anywhere - did the RC pitch a race that was completed? Does it pertain to all races in a series, or all races in progress (e.g. in a multi-class event)? There is no way to tell. OTOH, AP/A tells the sailors only Races not started are postponed (i.e. those completed are not affected). and No more racing today. That "today" happens to be the stated last day of the event tells them that the races won't be sailed at all.

My vote is to use N for races started, and AP for those not.

I would not use Code flag A flown on its own as it is used to communicate the following message:

AP over A is simple, communicates the message and doesn’t run the risk of unintentionally abandoning races in progress. 

Thank's a lot for your comments. I will copy the prescription from U.S. Sailing as this seems to be practical and clear.

Interesting. ap/h on boat then onshore take down and put up n/a. 

At our centre, we have solved this issue by using a beer flag. Not in the rules officially, but everybody gets the meaning. As the racers finish the last race of the day and see the beer flag, they know that racing has concluded for the day.

I once flew N over A to indicate no more races as the weather had deteriorated. The intent was that as boats finished (separate finish boat) and returned to the start line they would see and head home. One competitor saw the signal while racing and headed home believing the current race was abandoned. I do not use that signal anymore!
Usually I use AP over A and let logic prevail but I do agree another option might be useful

Let’s not over think this one. It’s not a decision of the Supreme Court. AP/A is the one. N over A effectively abandons your last race conducted, finished or still running. Not a good idea. 

Clarification for Ed Vincent - I don't read the N over A race signal that way - I think it means "N over A All races are abandoned. No more racing today" When read in conjunction with the schedule (last day)  it makes sense that that is the end of the event as there is no more racing possible on subseqent days.

Ben, that is what I wrote. Maybe I should not have added the aside. It obviously confused, rather than enlightened.

Paul de Groot gave the correct answer.  Below is a table that contains all the AP and N combinations:
 

I agree with Paul that AP/A or AP/H should be used for races that have not started and N/A or N/H should be used for races that have started.  However, if there is inclement weather coming in and you want all boats (racing or non racing) to go in, I suggest you display N/A or N/H because this avoid having to display of both the N and AP flags with a total of  5 sounds. 

A problem we have with the current rules is that we don't have signal that forces boats to return to the harbour.  This is why CORK, Kingston, Canada has the following instruction:
1.    SAFETY REGULATIONS

1.1.        [NP] When flag V over flag H is displayed with one sound signal all boats shall return promptly and directly to the harbour.  Further signals ashore.  This changes RRS 37

1.2.        RRS 37 is changed so that it applies when flag V or flag V over flag H is displayed with one sound.

Just like Mark, I would not display flag A as per US Sailing Prescription to RRS 32.

US Sailing prescribes that, if the sailing instructions so state, the race committee may display flag A (with no sound) while boats are finishing to signal that there will be no more races conducted that day.

AP over A is the signal that all sailors know, but it only should be displayed if there was an option to run another race.  No need to display it if you are finishing the third race and you only can run three races on that day.

Keep in mind that if you have multiple fleets with some in a start sequence and some waiting for their start sequence you should display A  (US prescription) or AP/ A over the class flag(s)

Peter-
With all (and then some) due respect, I disagree with you here. Your table and Paul's response disagree in that he states (and I concur) that the use of an N signal doesn't apply for races not started, that's the place of the AP signals.

I also do not consider the RC liable for responsibility expressly left to the discretion of the Person in Charge of a boat (RRS 3). While we try to keep our eyes on the weather and other such things that may affect the safety of the sailors - some of us to what has been described as a fault - it is still the responsibility of the sailors.

If there is a situation where it is preferable to run away and the potential exists to return after a threat has passed, AP/H or N/H would be the proper signal to display. Once it has been and all are known to be safe, then another decision can be made and displayed ashore.

Again, flag signals are the only RRS accepted form of communication between the race officials and the sailors without other event-specific forms described in the event documents. The lack of clear signals, acceptably displayed, can be grounds for redress and thus liability. It strikes me as a good thing for the sailors to make sure we agree upon and use the accepted form of communication to let them know what we're thinking and doing, without confusion or relieving them of the responsibilities they take on by participating it an event.

Again, I vote for AP signals for races not started, reserving N for those that have. Simple, easy, and clear.

Best,
-- Carl

Good discussions.  This is a great forum for learning about and interpreting our rules and we all should be thanking Paul Zupan for making this possible.

Carl, my reason for stating that N/A or N/H applies to races whether they have started or not is that under Abandonment Signals in RACE SIGNALS, the first sentence of text describing flag N is "All races that have started are abandoned".  The text in the other two abandonment signals starts with  " All races are abandoned".

Even though it has expired Q&A 2015.007 https://www.sailing.org/tools/documents/WorldSailingQABookletFebruary42016-[19986].pdf   supports my position.

I was not talking about liability here, but just safety.  Also, while we still have boats on the water we have to keep the CORK safety team out.  This instruction facilitates it.

The U.S. Prescription should be changed to "if the sailing instructions so state, the race committee may display flag A (with no sound) while boats are finishing to signal that there will be no more races STARTED that day.

Carl, according RRS 27.3, when N is displayed over H or A, applies (also) for races not started.

                                                 

RRS 27.3 clearly states that before the starting signal, the RC may abandon the race displaying N/H, or N/A. For abandonment after the starting signal, the RC may use N/H, N/A or just N (RRS 32.1).

RRS 30.2 and 30.4 also refer to abandonment before the starting signal.

Well, I would say I stand corrected, but I never said (and don't believe) that one way or another is wrong and another is correct. My position is that it is less confusing to display one flag in all its permutations under one set of conditions (e.g. N for races started) and another flag in all ITS permutations for another set (races not started). I advocate that this eases the confusion amongst the sailors some, and any help we can offer in that goal is likely welcome. It leads me to ask that why there are numerous ways, many described above (and the Beer flag is a good one!) to communicate the same intent of a Race Committee.

I confess that I was not aware of RRS 27.3, which makes me glad I don't do judging. Thanks to Myrto for pointing that out!

And I agree wholeheartedly with Peter on oh so many things, but specifically here in gratitude to Paul Z for setting this up and keeping it going. To paraphrase one of my mentors, we are all smarter together than we are by ourselves.

Thanks for allowing my voice.

-- Carl