It seems to me, that the breakdown of the non-verbal cue environment is frequently a function of fatigue.
After a certain period of years or after a certain number of routines are imposed, it just takes too much energy to demand consistent obedience. Unfortunately, this leaves those routines in a broken state, halfway between useful and purposeless. The students sense that lack of seriousness and the routines become mere speed bumps, occasional interruptions to be tolerated but not respected.
One of the very first principles we established for raising our daughter was to draw the circle of rules tight enough to cover the major infractions but loose enough to need only infrequent enforcement. This was based on the observation and belief that kids have considerably more energy to chafe against relatively pointless restrictions than parents have to enforce them. This leads to the “Don’t, don’t, don’t… ok” syndrome that eats many parents alive. We try to only establish rules that we are willing to us overwhelming force to enforce. If it is not worth a major consequence, it is not a rule in our house.
I have found non-verbal communication in the classroom to be somewhat ineffective.
On the one hand, it often does not get attention like verbal communications. In the case of the “quiet” symbol, it frequently takes a while for all the students to notice the symbol is “up” and quiet down. The noisier the student is being, the longer it generally takes to recognize the symbol, unfortunately.
This leads to the second issue. If the point of non-verbal cues is to provide information in a non-intrusive, quiet way, these symbols need to operate in silence. This is how it works in the military. On patrol, the only language is the silent world of non-verbal communications through commonly understood symbol language. Unfortunately, in schools, this is not the case.
Frequently, the “silence” symbol is accompanied by “shhh!” from the teacher and/or other students. More perversely, the “I want a drink” and “I want to go to the bathroom” symbols more often than not provokes a whole conversation between the student and the teacher. “Do you have to go now?” or “No, you have to wait, you should have gotten a drink at recess.” Both the silence and the class focus are broken.