When a diver turns it around it is an intentional act. You will never see a diver truly in distress turn the mask around. They are processing to many other thoughts for something that does nothing to make them feel better. The act of turning it around is simply a way of displaying to others you are in control and not under duress.
As mentioned earlier, one small sign of discomfort, or early signs of stress, is getting the mask off the nose and pushing it up onto the forehead so the person can breath more naturally. It is a natural act and a very large percentage of divers will do it at one time or another. Over the years, those that did not pay attention in class, were trained poorly, suffered from CRS, or just overheard part of a conversation linked the mask on the forehead immediately as a bad sign. As new divers became instructors, and only remembered pieces of their trainings the mask on forehead became taboo.
The mask on the forehead is not a universally recognized symbol of a diver in trouble as taught by some. It is simply a small sign a person will see early in stressful situations, the properly trained personal will notice it, assess the situation quickly and either start watching a bit closer, start moving in for assistance, or (and here is the part they all seem to forget) check off as natural and return to their normal activity.