At a conference the other week I picked up a couple of coffee mug coasters at the USA's NEI (National Eye Institute, nei.nih.gov). These are 10cm sqares of 3mm neoprene with blue material cating one side and white printing of the logo, name and web address. I thought they might be useful for patching a wetsuit or the like. If anyone wants to ask the NEI where they got them from...?
Most divers on a day boat, at least in the warmer climates where many congregate, will wear a T-shirt before/after a dive so that's the best item to get attention. Certainly Amphibious Outfitters have a serious corner of the market in Florida.
I could see me Aquasealing a patch to my dive case/bag, BCD or suit. If it were made of reflective material, then that might be a selling point too.
Another thought - a suitably waterproof keyfob would clip to a BCD ring..?
Or, how about carrying your very own Scubaboard branded body bag? Really cool way to impress the local coast guard/coroner, but better hurry up before the DIR crew think of it...
K.