.... Check with the authority .....
...Lastly, request a written copy of any 'No Metal Detecting Policy'.
HunterMF, from what you have written so far, it seems you've found a definition of your exact place. The closest that could apply is "preserving history". But heck, I bet that ANY city our county or state park's boiler-plate verbage ALWAYS has something about cultural heritage, etc... But realistically speaking, that's for protecting obvious historic sensitive monuments. If the day came when we all assumed such verbage automatically precludes md'ing, is the day we'd immediately cut off most of our detecting spots. Because I can't think of any city where if you were to walk in and ask "
Hi, can I disturb and take the history please?" that they're going to tell you "sure, go ahead".
If you don't feel that the text you've found constitutes a list of rules, then do NOT do what hvacker and stefen suggest. Which is: To go waltzing into bored pencil pusher's offices talking about metal detecting. That can result in a "no". Ie.: the whimsical "safe" answer . Because maybe they think you'll harm earthworms, or leave holes, or whatever. Ie.: the old "no one cared....
UNTIL you asked" routine.
Instead , if you are skittish, find the park rules online. Or if you can't find this list, then you ask "where can I find the rules of the park listed?". Eg.: dogs on leash, no alcohol, no fireworks, blah blah. If you see nothing there that says "no metal detecting", then presto, it's not prohibited.
I've detected many such sites as nature preserve and OS places where the public is not prohibited from being. Never had a problem. Perhaps I didn't ask enough bored purist archies, but .... just sayin'.