I'd take that a step further, and discuss what signals _you_ and _your_ buddy will use for the dive.
Don't assume that because you hear of some signals considered 'common' on a web board, that the next person you dive with will use them or understand them the same way.
Discuss signals and review them in the pre-dive discussion. Don't assume
To the OP ... as you can see, underwater language is a multi-lingual thing. So whatever signal you decide upon, the most important thing is to make sure ... before the dive ... that your dive buddy knows what it means. Otherwise it'll just create confusion.
When all else fails ... everybody knows that the thumb pointing toward the surface means ...
... Bob (Grateful Diver)
Yes, I will definitely be discussing signals with my buddy, as well as issues like, If I start to go right and my buddy starts to go left, which of us should follow the other.
In fact, since my upcoming trip is a live-aboard (Nekton Pilot) I am going to raise the issue of signals when they give us the general orientation, and see if the group can reach a consensus for the week.
As I mentioned before, I know that I can end the dive at any time for any reason, and my buddy or DM can do likewise. But if communication can resolve an issue safely without ending the dive, that's always a good thing.
(As a former ham radio operator I have thought that it would be great if all divers learned Morse code, but I found a thread here about that, and I see that there's no general agreement, with concerns about noise pollution, etc., and a counter-suggestion that all divers learn ASL, and disagreements about that also. I do carry a slate, though, which is great for asking "What's that?")
Oh, the other useful signal (which I would be using all the time) would be one for "
WOW!!!!!!!!" There are times when a simple "ok" sign is just not emphatic enough. But maybe that's just because I'm still so new at this.