I wonder if this type of nonverbal communication is still prevalent in the large, noisy factories and sweatshops of the developing world! This would be an incredible research project.
It exists today in steel pipe mills in the US, where the noise is such it is impossible to hear a voice -- even shouted -- from further than a foot away. Radios are similarly useless due to background noise, so a catalog of hand gestures are used to communicate across the factory floor. It is almost impossible to communicate the wall of sound in one of these factories with words.
On a side note, I would be curious to learn if this improvised sign language is consistent between mills, or regions.)
In these same pipe mills I saw another curious method of communication which the employees referred to as "Mexican radio". (This was in south Texas where the preponderance of employees were Latino). The worker at one end of a 40-50 foot long pipe would put his ear to the end of the open pipe, and the worker at the other end would yell into the pipe. It worked surprisingly well (frankly better than yelling from a foot away into open air) but the safety officers weren't too keen on the idea as it put soft body parts (faces and ears) next to potentially razor-sharp pipe ends. Hand gestures were preferred and crossed any English/Spanish language barriers as well.
I worked in a printing press ten years ago, and all of the pressmen and binding-machine operators were deaf (congenitally, not from the equipment) and thus fluent in ASL.
I'm not sure if management sought them out or if one guy got hired and started recommending his friends, but it worked out well. They could communicate with one another perfectly in places where even shouting was inaudible, and they often seemed to be better at communicating even with people who didn't know ASL just because they were so good at nonverbal communication.
I learnt BSL (British Sign Language) with my then girlfriend whilst at uni. We used it to chat in the library, talk to each other across the room anywhere it was too busy or inappropriate to shout - very useful.
Given the access to information nowadays i imagine people would be more likely to learn an established sign language due to its wider use. That said we developed our own simplified signs for BSL to communicate with our babies, which quickly became adapted by them, so even this way I feel slangs would develop readily.
