ok wise guy, you just opened a can of worms: Suppose if, in states/cities with such a law, that someone finds a diamond ring or gold bracelet in a sandbox or beach (not a un-common possibility, eh?) that's easily got a sales-counter value of at least the given benchmark amount?
Such was the case of a recently circulated story in the pacific northwest, where a couple eyeballed a diamond ring in a grocery store parking lot. They took it to a jewelry store in this small town, to "see if it was real". The store ... after some rigamaro .... recognized it as a "be on the lookout" item they received word on (to see if it turned up in a pawn shop or jewelry store, etc....). They called the police, who paid a rather .... uh ..... "unpleasant visit" to the finders. The finders tried to say "we only found it" and "we weren't trying to sell it, we were just checking to see if it was a real diamond", etc.... In the end, the couple got in trouble for JUST the type laws you cite: that found property over a certain dollar value, don't just simply go to the finder (ie.: "finders keepers" rule). That has some very INTERESTING ramifications to md'ing, esp, jewelry hunters, eh?
The law states (if you want to be technical), that you must turn them in to the police station, and if no one claims it in XX number of days, you can keep it. But man, I'd be afraid some corrupt police outfit would merely inform you at the end of XX days "it got claimed, scram"