Nice, the way you incorporated their official logo. No telling how a ranger might react. Laugh and leave it, not notice it, call in to ask if its real, take finger prints and go looking for naked people because it impersonated law enforcement...who knows.
Since there are no fed laws, it isn't incorrect. The state law is concerned with alarm, or reasonable affront. Unless they can attach you to the sign, you now should have no problem. The laws and the official sign should replace the need to clothing, it is a license to be naked and have hassle free fun. It should be seen as a prank and they might remove it.
Maybe I should get me one and a pair of plastic gloves. I could post at each trail-head, and eliminate the need for back up clothing, or concern. "Hey, didn't you read the sign? This trail is officially clothing optional."
If the best idea is to not stir up complaints, then this might not be a good idea in other states...or it might be a good idea.
Jbee