It is not a sign of distress. Never has been. It has been falsely taught that it is.
Is MOF an absolute and universal indication that a diver is in distress? No more so than having a temperature is an absolute and universal indication that someone has pneumonia.
However, categorically saying "
It is not a sign of distress. Never has been. It has been falsely taught that it is" sounds just as ridiculous as anyone who categorically says that MOF is an absolute and universal sign of distress. (Although, while there's no shortage of people in the former group... in ten years I've never met anyone in the latter.)
It's quite possible that someone either has limited experience in real-world diving situations or has simply been lucky enough to have never seen a diver in distress reject their gear upon surfacing - spitting their reg and pushing the mask up off their face. In the real world... it happens. Not universally, and not always in the same fashion. Sometimes the mask comes completely off, sometimes it ends up on their forehead, sometimes it gets pulled down around their neck.
Accordingly, I'll speak to my own experience:
Yes, 99% of the divers I've seen surface and put their MOF were fine. I only know this, because I spent 2 extra milliseconds looking for other potential signs.
However, >50% of the genuinely panicked/distressed divers I've encountered in the real world have surfaced and immediately shoved their masks up off their faces. I only knew they were panicked/distressed because I spent 2 extra milliseconds looking for other potential signs. I guess if they had trained with Jim they would know that their technique was wrong... and that they were supposed to tear their mask off completely and scream.
One of the most instructive incidents involved a victim (yeah... he became a victim) who surfaced after a successful CESA demo, fist-bumped the instructor, and settled in at the surface. A moment later, he pushed his mask up on his forehead and gazed towards shore.
One of our other students -
all of whom are taught that a diver rejecting gear is one of a number of possible signs of distress - said to him "John... you ok?" This got the instructor's attention, who turned towards John just in time to see him go face-down in the water, completely non-responsive. (After the incident the instructor - and others present - stated that if he hadn't heard someone say "John... you OK?" he would have assumed John had simply put his face in the water to watch his son who was down on the platform about to do his CESA.)
Long story short; after a tow to shore, full activation of the quarry's emergency staff, an ambulance ride to one hospital, a helicopter ride to another, and a few days at the UPenn hyperbaric center John is fine... because someone had been taught that MOF was
one of a number of possible signs of distress.
If the other student had been taught by someone that "MOF is not a sign of distress. Never has been. It has been falsely taught that it is" John would probably be dead right now.
Accordingly, when I see a diver surface and remove their mask I'll continue to take the 2 miliseconds necessary to look for other signs of distress. I will continue to spend the 20 seconds necessary to convey the rationale for doing so to students. I will continue to ask any diver I'm diving with - student, buddy, or otherwise - whether they are ok if I see them push their mask up on their forehead. If they say "yes" I'll simply say "be careful you don't lose your mask" and go on about my business.
Doing otherwise seems irresponsible.