I've heard that the gay community has a "hanky code" where the color and placement of a handkerchief identifies them as gay and says what they're looking for. Watersports, naturally, is signaled by a yellow hanky.
So what we need is a signal that we can all use. I know Patches Place used to sell what they called the "P-Shirt" which was a tee emblazoned with "I love wet patches" on a sploosh-shaped backdrop. That might be a little [i]too[/i] blatant.
Something in between, though, that makes it possible for us to identify one another without tipping off the rest of the world, would seem like a Good Thing.