Correct, TigerFanatic .... and in some states it is a law that boats of certain lengths must carry a whistle (or other signalling device) to indicate distress. I would assume that a simple morse code SOS ( ...---...) blown out on a whistle, would be recognizable as a distress signal by most people.
I have one on my boat's kill switch lanyard ... but, I think I will take your "advice" and put one on each of the PFD's, as well. Thanks for that suggestion !!
... cp