Can you tell if a map has been used?

I picked up a map somewhere. I don't remember how or when. According to the wiki, there is a chance to discover a quest while reading it; that is, it's not immediate and automatic the first time someone reads it. As I said, I don't remember how long it's been in the colony, and I'd like to sell it if I've learned all I can about the quest. The problem is, I don't know how to tell whether that's true. Any tips?