I was taught that it was a sign of possible distress, but along with things like being wide eyed, or breathing heavily, we were taught that it is one of many signs that should be taken in context. For example, if my buddy was wide eyed and breathing heavily after an encounter with a mermaid, I would presume excitement rather than a problem. I might still double check with an "OK?/OK" though.
If a diver surfaced suddenly and alone, forgot to inflate her BC, either removed or lifted her mask, and seemed to be having difficulty, I would be inclined to take the lifted mask as reasonable indication of distress. If I saw the same diver surface normally, inflate for positive bouyancy, lift her mask, and with her buddy begin a leisurely surface swim toward shore, I would not.
I was taught that it's a possible indication to be taken in context, not that it's a distress signal. There's a big difference. If someone who didn't need assistance was waving a safety sausage or flashing a mirror and blowing an air horn, I would consider that reckless. If someone has a mask on their forehead, that's a different kind of thing altogether.
IMHO, if someone mistakes my lifted mask for a distress signal, they either didn't understand the assessment lesson, or were taught differently than I was.
I did say "distress sign" in my prior post, and apologise for the confusion. I meant signal, and have edited it.
