Not speaking on the surface might also be a sign of distress...This one of those Scuba Myths that will not die.
The danger of a mask on a forehead is losing the mask.
Essentially EVERYBODY put their mask on their forehead in days past; just look at old pictures of divers.
It isn't so much that the mask on the forehead indicates distress, but it might. Taking the mask off may indicate distress too.
and when the boat finally gets around to coming around, down goes the mask and into my mouth goes the reg
until my bum is in the seat to quote