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.