I read a while back about someone who found some bags of maney (Canada). He/she (you can see I didn't read it very closely) took it to the police who waited (I can't recall if it was three or six months). Anyway, no one claimed it. The money went to the finder. (I expect they thought there might be illegal dealings involved and that was why no one claimed it.) The folk got a chunk of change, free and clean.
A diamond ring--if it is indeed diamond--can be real expensive. And I may have some seriously sentimental value to the person who lost it. It would be nice if the young man took it to the police.
Oh, I found a Mercedes today. I can figure out why the doors were locked and there was no key in the ignition. However, it runs just fine.