Here in crowded coastal waters with a lot of shore lights, I doubt anybody would take much notice of another flashing light even if it's extremely bright in a pattern. If they noticed, they still might not recognize it for emergency signal. However a red flare definitely would get boaters to call the CG. Or orange smoke during the day.

I think if you really want effective response, coastal, you need VHF communication or pyrotechnics. JMHO.