I picked up $230 in cash in a cab, it belonged to a chinese
woman who slammed the cab door when I was about to board it after
she alighted.
I didn't return it; because she was rude, and there was no IC
inside.
I found a wallet with about $100 outside the women's toilet, I
handed it to the information counter and had her paged to collect
it.
Basically my rules are simple; if there are identifying IDs or
cards in the wallet, I'd return it. If not, and it's found in a cab
I'd notify the cab company.
But if the amount is huge, such us $40K, I'd know someone's in big
trouble if I don't return it - so I will return it.