One handed sign language/control/ gang stalking

I was reading this article on gang stalking and it repeatedly mentions "one handed sign language".

I have noticed people signing/making symbols/gestures at/towards me that I am unfamiliar with and can't find much information on this.

The only person I have ever seen talk about this is Zack. I thought he was nuts but now I can see when people make these gestures/face touches.

Wtf does it do/what is the purpose?

I know that seeing things can cause people to react certain ways (like seeing 2 girls one cup makes most people cringe or squeal automatically), is there something neurologically that happens when we see people make certain signs with their body even when we are not familiar with the purpose or reason?

Just some questions for my fellow fingers :) thanks.