The "Y" flag. 

ICS Yankee.svg

When shown prior to the warning signal, or ashore, this flag REQUIRES use of PFD while afloat.  If you do not comply, you are DSQ.  See RRS Rule 40 below.  All sailors should be aware that the Coast Guard has issued the final report on the Dauphin Island tragedy four years ago.  A copy has been posted on this web site under the Right side menu item "Read this stuff".  The recommendations to US Sailing for rule changes mean that PFD's are about to become much more of our life.  We will review this and try to come up with a workable solution that you can live with.  As a minimum, we will use the "Y" flag more often, as appropriate.  This is serious.

"40 PERSONAL FLOTATION DEVICES When flag Y is displayed with one sound before or with the warning signal, competitors shall wear personal flotation devices, except briefly while changing or adjusting clothing or personal equipment. When flag Y is displayed ashore, this rule applies at all times while afloat. Wet suits and dry suits are not personal flotation devices. "

Because we do not have shore facilities, our SI designates as follows.  "5.1 Signals prior to the normal sequence time shall be displayed aboard the Race Committee boat, which may be at the Villa Capri dock or in the racing area.  "