The city I live in has a "no dig" law. Some of the Park Rangers seemingly could care less and drive right by me, cops, too, but one guy has caught me twice plucking clad drops with my screw driver off of a festival site that has a arts and crafts event once a year. Usually good for $25. -$35., lots of quarters lost, over 5-6 hours of hunting. The Ranger guy was always nice and explained there is no law against metal detecting, but digging of any kind is against the law. And, if you should find anything, it needs to be turned into the city treasurer. Park maintenance personnel usually cleans the spot of all liter Mon. after the event and I get to then Tues. and Wed. a m early. I've been caught twice over about a 15 year time span.
Obviously, I can identify with you Old coin hunter as far as the b s of public spots being off limits, but the festival spot is not Federal, either. HH Jim tn