Obviously The Role

If anyone's wearing all black, they're evil; if they wear all white, they're good.

You can tell what role someone might be sometimes just by simply looking at them. No dialogue is needed, no backstories, just knowing what their physical appearance is like is all it takes. This is in part due to how a character can have a cliched look to them, like how a man wearing a trenchcoat, sunglasses, and a shady fedora would easily be the Dealer and nothing else (unless our expectations were gotten).