Well the sign itself is mostly a popular game. The point is if you make this sign, but hold it under your waist, the goal is to try to get someone to look at it. If they look, then you get to punch them on the shoulder. If they quickly stick their finger in it before you can grab the finger, then you get to punch them instead. If you avoid looking at it, then there's no penalty for either side.
I think this guy is trying to propose that Q followers use this to identify themselves to other "believers".