What would make you assume someone you just seen once taken

I really don't.

Some people assume those they find very attractive are taken just because, to them, how couldn't they be? Of course they are!

A wedding ring.

wedding or engagement rings.

Someone who is in physically fit and attractive, intelligent and articulate in their speech who isn't attached is a rare thing to see. So when I run into someone like that I assume that they were probably done wrong by someone of likely similar qualities, but lower standards of conduct. So they are now not easily, if at all, going to get involved again.

People are always perving on me and people assume I'm taken, it doesn't stop thoughts! I do check men's fingers though and smile when there's no ring.