My favorite "confusion factor" sign is the caver's "I'm stuck" sign, which means "I need to go to the bathroom" in ASL. Maybe both mean "I'm in a tight!" Then again, if ever there were a "context sensitive" sign, that'd be it.... I know many cave divers who use some ASL signs when they make sense,...
Rick
P.S. I teach the one-handed "cave" numbers in the very first hand signals lesson during OW training.