Re: Seriously ER
I don't know. I've never been in a demonstration. I smelled tear gas once and that was enough to convince me I wanted no part of that scene.
I assumed it was some kind of communications exercise for crowd control, it seemed a reasonable assumption, particularly since it seems this video was recorded by movement organizers for distribution to their followers. Maybe I'm wrong.
But I know about hand signals, I had to learn them to communicate with riggers handling deck cargo.