World Sailing Regulation 20 - Advertising only covers “boats and competitors”.  I don’t recall any Regs limiting ads on RC/AO property. 

Thanks for that. You see my problem! 

I've seen a lot of advertising and I am also using our starting vessel for some advertising. It is important, that banners and flags are far away from signal flags and everybody will be more than happy. 

I've done quite a few events from beer-can to major Internationals both as official and a competitor and in quite a few countries, and I cannot think of a single one where there was no sponsor flag on the RC and other official boats. The sole exception being where there is no sponsor!

It is my club’s standard practice to only purchase marks with clear ad pockets, including the start mark. Sponsors seem to like it and it keeps the signal boat clean. 

Andy … looks like you are only limited by good sense and good taste! :-)

Not current information but when I used my boat for RC Signals during the Pan-American Games in 2011 I was required to have sponsor banners on the boat. I was not happy about it but there is no rule I am aware of then (or now) that prohibits it.

This is a pin boat on a regatta in Brazil (I think). The only limit is your imagination.

According the terminology section of the RRS a boat is “A sailboat and the crew on board” so a signal vessel is not considered to be a boat and this code would not apply to them. 

Provided that the advertising on the sponsor supplied RC boat doesn't interfere with seeing or hearing race signals or RC tasks it should be welcomed as great support for the event.

Cesar … can you imagine the insurance claim if a boat hit that truck!!  

Insurance Adjuster: “Your truck was WHERE and got hit by WHAT?!?!

Angelo,
That would be funny to see. Even for the Protest Committee in case of a protest. Facts found: the boat hit a car on the starting line, hahaha, so much fun

Adjuster: SleepSoundly Insurance .. how may I help you?
Owner: Yes, I'd like to make a loss claim on my truck.
Adj: Where did the loss occur?
Own: About 2.5 nm SSE of the Bay Bridge
Adj: What was the name of the road?
Own: Uh .. well ... there was no road .. that's a location on the water.
Adj: On the water?
Own: Yea .. on the water.
Adj: Did you drive your truck into the water?
Own: Uh . no .. I drove the truck onto this little barge you see .. then we towed the barge and truck onto the water and anchored it in the middle of the Bay.
Adj: Uhhh .. OK.  Why did you do that?
Own: Well .. we were using my truck as the pin on the starting line.
Adj: The pin for the starting line?  What starting line?
Own: Well .. the starting line for a sailboat race with these big boats .. maybe 20 or 30 of them ... 
Adj: Uh .. huh .
Own: Yea .. so the way this all works is that the sailboats take this running-start … well … they aren’t running … they are sailing … but you know. … this running-start at this imaginary line we call the starting line . and my truck on the barge was one end of that line.
Adj: Uhhhh .. OKaaay..  Soooo ...  you put your truck on a barge, towed it into the middle of the Bay, and anchored it in a location such that 20-30 big boats sailed right at it at full speed?
Own: Yup
Adj: Uhhhh ... 
Own: Well .. you know there are rules .. they aren't supposed to hit the pin with their boats ... and my truck and the barge were definitely the pin .... that's the rule you see .. it's all right in the uhhh rules .. uhhh ... yea .. here it is .. Rule 31 .. 
Adj: And one of these boats ran into your truck?
Own: Well .. technically .. it ran into the barge and they broke rule 31.
Adj: So the boat didn't run into your truck?
Own: I'm not sure.
Adj: What do you mean you're not sure?
Own: Well .. I'm not sure if you can see any damage on the truck from the boat hitting it
Adj: OK … well  .. can you go out and look and take some pictures?
Own: No .. unfortunately I can't.
Adj: Why not?
Own: Well I can't actually see the truck or know exactly where it is .. you see the boat hit the barge, the barge tipped over and dumped the truck off the barge and now its about 30 feet down at the bottom of the Bay somewhere.
Adj: [silence]

That is hilarious!!!!

Our regular race committee boat was ?donated, ?supported by the local water authority who own the lake.  It has their logo on it.

Events will often add the sponsors name to the event... "Rolex Fastnet Race" for instance.

Prada sponsored an America's Cup. 

https://images.app.goo.gl/SgL6UpuzwYPWToSy9

That said... Is the sponsor aiming to be seen by the sailors or the "press". Press pictures seem allergic to showing committee boats! And if they do, it's often a line of 50 boats about the start with a miniscule RC boat too small to see the sponsor...

Lots of clubs in Australia have advertising on committee vessels

Get the PRO to make up the loss in revenue if he doesn't want the sponsorship.  Running regattas is expensive and beggers can't be choosers these days.  Its great that you have a willing sponsor.

I think you may be asking the wrong question. Advertising is not the issue here - plenty of precedent to allow it - in reply to your PRO - it is done regularly. 

We need willing sponsors in sailing, a banner is not going to interfere with the race management - get it up