> "It may be your right (or not, I don't even know)."
No. This is stealing. I cannot imagine a modern legal system that would not recognize it as such. "How did you acquire this wallet?" "Oh, I found it in the street!" "Oh, no problem, then. It's yours."
Ok, fair enough. But again, what's legal and what people do are very different things. You'd be surprised how many people would just keep it.