I can't say this with absolute certainty, but copper culture is part of why Wisconsin has some of the worst public access laws in the nation. There was a push about 10-15 years ago to get legislation on the books to allow for more detecting on public properties. It was making it's way through the various committees, but then Native American interests stepped in and the bill died. Their attorneys pointed to ebay listings for copper culture artifacts that claimed to be found metal detecting in and around Copper Culture State Park. After that, no legislator wanted to be associated with the bill.
Some time later, the DNR's archaeological person strictly interpreted the law on the books and prohibited detecting on state properties without a permit, and the only way you could get a permit was by requesting one from the property manager to look for a *specific* lost item that has to be described on the permit. You are supposed to turn over anything you find that's not noted in the permit, and anything over 50 years old or older is considered an artifact of the state. So yes, that 1968 Lincoln penny is off limits.
I should add that this gets even weirder. If you're recreationally prospecting for gold or other metals, you can allegedly use a metal detector in addition to a gold pan or other methods. Hey, I don't write these laws, I just read them...
