We have a similar law here in Michigan, but I have never heard of it being enforced upon metal detectorists. I think the main point of such laws is to prevent actual thieves from using the excuse that they "found" any items in question in order to prevent prosecution. With this law they could still be facing charges for not returning such items to police.
All that said, I still make an effort to return items that I have found if they have identifying marks (Names, class rings with initials, etc). I look at lost jewelry with ID the same way I look at a lost wallet with ID. I'd never think of keeping a wallet full of money if it had someones drivers license in it, why would I keep a bracelet, ring, etc if it was easily returnable?