And what would you base you educated guess on?
For the time being, I base it on ethnicity first and foremost. Choice of apparel is a often a factor. Behavior can be a factor. If I can't tell, there's little else I can do. But I make judgments all day long about many people and for various reasons. For instance, someone stole a bike, took it for a joyride, and dumped it across the street from my house a few days ago. I called the cops and they picked it up. If I watch for possible culprits, am I going to be looking for a man in a business suit, or for a bunch of teens walking down the street yelling profanities?