I have seen several instances where uncomfortable divers in the water have simply pushed their mask up on the forehead or down to their neck. I like to explain to students that it is inconvienent to lose and it is a sign ( a sign is something you see in others) that they are in control if they have the presence of mind to properly and safely secure/stow it against being lost by doing something. They give me the OK sign and do something rational like safeguarding equipment there is a pretty good chance they really are OK. The mask on the forehead is something that will cause a little more scrutiny before I decide.
Now one time discussing hand signals in a class did cause issues when a five year old had come in to the classroom unknown to us and ended up shooting the bird to her mother later that night.
Is the "OK sign" they show you on the surface, the fist on top of head, or is it the OK sign we all use when we go under water?