It's just part of the same old story. Park Rules were written long before "Preemption" and they just keep posting the same old rules. Doesn't really matter because the "No Firearms" portion is unenforceable provided the carrier doesn't discharge his firearm or violate RCW 9.40.271. The County Parks Department will continue to put this "no firearms" logo on the signs until the County Attorney tells them to cease. Even then the signs will remain up until they are unreadable.
With all the budget crises around the State, I doubt anyone will go to any great effort or spend any money to erase these unenforceable warnings any time soon.