The Assistant Village Idiot has three posts up about sending signals

Social
By Politicians
Among Friends

Let me quote a bit from the first piece to give you the flavor.

Sophia has the office next to mine. She is a Christian conservative of slightly different flavor - chocolate chip to my vanilla, perhaps. Her window looks out over the copier, and she has affixed a long list of examples from around the world of what bad things happened to peoples who were not allowed to own guns. It's been up a few months. I don't know how many folks have read it.

One of the med students from another unit brought the psychiatrist over to look at it. Neither said a word, the younger just pointed to it and grinned mockingly. How do I know it was mockingly, rather than approvingly? Because our brains are very good at picking up social cues like that. Even the worst of us are pretty good at it. We evolved in groups where such things were important for survival. Tribes enforce their norms via gestures and expressions which are maddeningly difficult to describe.