Yes, but do we know where MOF theory originated? Was it ever in print?
I can't speak to the beginning of the concept, but I think I can tell from my own experience as an instructor how it became so popular.
First of all, we have to understand the difference between a
signal and a
sign. A
signal is something you do deliberately to convey information to others. A
sign is something that others see in you that leads them to draw a conclusion. A panicked diver does not intentionally
signal anything except perhaps shouting for help. There are, however,
signs you can spot that can indicate growing panic.
The PADI OW course I taught from the mid 2000's described
signs (not signals) that would indicate a diver is panicking. Those
signs include equipment rejection, like throwing away the regulator or shoving the mask up . A mask shoved haphazardly off the face could be a
sign of panic.
The final exam for the OW course had a question that asked which of the following choices could be a sign of panic. The correct choice was a mask on the forehead. An instructor teaching a class would want the students to do as well as possible, so he or she would likely stress that point, especially in the final review before the exam.