Re: I have had some similar incidents.
We've been lucky enough that almost everything of real value we've found has had some sort of ID that makes it easy to track.
To be perfectly honest, there is a lower limit. If I find a dollar on the ground, I'll wave it around and see if anyone close by may have dropped it, or check at the cash register if one is nearby, but if nobody speaks up, I keep it. Same for loose change. If I found a hundred dollars and nobody claimed it, it would go to the cops. Not sure exactly where the line is drawn...I suppose it depends on circumstances.