I was in the parking lot of a large supermarket yesterday. As I returned my cart to the corral, I saw a folded $20 on the ground. I picked it up and looked around. No one in sight. I looked around the corral. No driver's license or wallet or anything. So I just kept the money. If you found $20 on the ground, would you feel an obligation to try to find the rightful owner? What if it was $100? Surely you don't have to trouble yourself to figure out who dropped $1, so what is the amount at which you should make a significant effort (like go to the police) to find the rightful owner? If you realized that you had dropped $20 at a supermarket, would you go to the front desk to see if anyone had turned it in? The funny thing is that I've seen people drop money before, and I've always pointed it out to them. I don't think I've ever found a sum of money larger than a couple of dollars.