First, assuming you mean 29.1 in the header not 28.1? RRS 29.1 is clear that the X Ray and additional sound is at the start signal. A competitor in breach of 30.1 has until the start to cross an extension so the RC does not have to display X Ray until the start signal arrives and the competitor has not exonerated him/herself. If the competitor crosses the starting line within the last minute before the start and returns to the pre-start side via an extension in the last minute no signal required. 
Supplementary question: Who uses India and why? 

Nick,  First, thanks for the correction to the rule reference.  Corrected in OP.

I don't think that 'RRS 29.1 is clear that the X Ray and additional sound is at the start signal' when Flag I is displayed.  Otherwise I wouldn't have asked the question.

It appears to me that a boat's obligation to comply with RRS 30.1 and sail back across an extension, begins at the time the race committee observes her on the course side, and RRS 29.1 provides that 'When ... [a boat] must comply with RRS 30.1 the race committee shall promptly display Flag X ... .