Very similar 'codes-that-aren't-really-codes' in many UK town and borough parks & public spaces. No specific bye-law regarding drones, which can be challenged by asking for a Judicial Review and judges ruling... but threats to hammer the drone...
I googled a bunch of links (here's just a snippet of my search history) and I quickly figured it out thru my experience with similar legal matters so it's just my opinion on this, not legal advice. Wasn't difficult for me to figure out what they...
Yeah I check it. That sign is absolutely and completely enforceable and if you fly your drone there and you show the police a piece of paper, you'll likely still get in trouble. Local agencies like cities and counties are KNOWN to post code...
Geez, did anyone bother to check the Placer County Code?
I did. Here's PCC 12.24.020(A):
That's it. nothing about drones. The sign is in error, probably wishful interpretation by either a private citizen who made the sign, or a park official...