Shit, I'll be honest and say that I have a pretty good moral standing on lost property. But I also have a severe distrust in others, and shit... I know my double view on morals, so I know what others will be thinking.
Loose change, no matter the amount, is mine. Anything with identification on it, then no, I'll make an attempt to return it. No way to identify? Even if a couple g's... mine. I might make a stop at a nearby police station if its a couple thousand, but I'd be cautious in my explanation, and wouldn't turn it in or even state I have it. I'd question if anyone has come in looking for lost money of that amount. And probably leave a contact of some sort.
And that's also one reason I don't like dealing with cash of my own. And if I lost cash, I would basically just forget about it, and if worth a lot, make a stop at a police station but never expect anything. Also, I'd never expect anyone passing cash to leave it, and thus if I saw it... might as well claim it as mine, because the next guy is going to want it, and quite possibly a few will be looking at it as a chance to score their next fix.