Many regattas I have been to in my life (or was it just Hobie regattas?) fly a lifejacket-required flag when the wind is over a certain level. I don't even know what it looks like because I ALWAYS wear a life jacket, even if there NO wind.

Our Hobie fleet in Miami used to have a rule that if there was enough wind for you to go out on the trapeze, you had to be wearing a life jacket.