Is there a hand signal for Acknowledge that does not also try to indicate "I'm okay"? The Okay symbol to me seems like the wrong response to another diver that is in trouble.
Diver 1: Hand signal for Something's Wrong / signal for Up.
Diver 2: Hand signal for "I'm Okay"
Diver 1: ??? It's great that you're okay, but I need help / need to surface to fix problem.
so there are two types of signals, and I think this is what is being said above. There are normal signals; look, shark, that way, question, problem, turn around, etc. These do not require a response.
Then there are the command signals; OK, Hold/Stop *clenched fist btw*, and Up *thumbs up*.
Command signals, in your case the "Up" signal, requires the up signal to be returned as the same signal to acknowledge the command. There is no other response to a thumb when in the water. In a cave it means we are leaving, do not pass go, do not collect $200, we are outa' here, as opposed to the turn signal which means let's start meandering back to the front but if we see something cool we can poke around. In open water it obviously means we are going up to the surface, and going now. Same with "Hold/Stop". You don't have the luxury of any other response, if someone says stop, you acknowledge that command with Stop.
OK is a little different. It is still a command signal, which means it requires response, but it can get different responses since you may not be OK. Acceptable responses for me are "OK" or "Problem".
So the signal progression, as mentioned above is as follows.
1: Hold
2: Hold, and maybe "question"
1: problem *open hand rotating side to side*, point out the problem, and potentially ask for help with something if it is fixable *gear problem they can't reach or something like that*, if not like ear pain or something like that, then just go up.
1: Up
2: Up
when at surface, then ask questions, though on the ascent or on safety stop, 2 should ask 1 if he's OK, which then requires either *OK* to be given back, or the *problem* signal and point to the problem again