Veritas, first thank you for your service; police are all too often put in a bad light when they are indeed true heroes.
I am not too keen on law, so I took a peek at the links below
http://www.legalflip.com/Article.aspx?id=8&pageid=21
https://www.lawnow.org/all-is-not-lost-law-lost-and-found/
I would argue that a disc is under the category of "lost", not "abandoned" nor "misplaced". That said, the original owner is still the rightful owner. In addition, if the finder refuses to give the disc back, it is theft by finding; thus he is liable on both criminal level and on a civil level should the disc be damaged. If the owner cannot be found (ie: unlabeled disc), then the rightful owner is actually the property on which the disc was found. See the second link's case references.
Moral of story: if you find a disc and you don't try to contact the owner, use the lost disc boxes. If the rightful owner doesn't attempt to retrieve the disc, then it is considered abandoned and the finder then and only then gets the disc