I believe we broadcast information about ourselves
I'm really good at reading complete strangers.
Just the other day I saw a man and a woman walking and I said to my mother that they were police, despite no uniform, badges or gun.
As they got closer I could see that the book he was carrying had a police logo on it. I had them picked as police in less than second of glancing at them, and at a distance.
When I worked in LA I could tell the difference between an american of latino origin and a latino foreigner.
It's as though they broadcast something about themselves and I get that signal.