Love the energy yang

I’m sure this is a really dumb question, but when you see “Pass Left” or some other text from someone, how do you know which car they’re in? It says their name and I think their number (I’m not looking at it right now) but I don’t know which person is in which car. Or the reverse: when you see a car, how do you know which person is in it? Sometimes when I let someone pass, they’ll even thank me by name, but I don’t know how they know who I am! That would be a useful thing, it would be nice to thank (or scold) people by name