The common hand signals (OK, not OK, up, down, turn around, I'm cold, ear hurts) seem to be the same in all parts of the world in which I've dived. The ones that always seem to differ are stop (flat hand vs fist), question (little finger vs crooked first finger), go that way *use of thumb vs first finger to point), what is your gas pressure (two fingers tapping SPG or palm versus holding up the SPG), indicating pressure (many different ways), Fish species are another highly variable sign, except for moray eel, octopus, shark, and frogfish. Seahorse is a crooked first finger vs a riding horse motion. My favorite is the sign for a hamlet, where the diver holds lout his hand like he is holding a skull in front of him and looking at it.