At Federal recreation sites that don't have entrance stations you need to display your pass or show proof of pass ownership to compliance officers via one of the two following methods:
A pass can either be displayed on your rearview mirror using a free hangtag or on your dashboard with the signature side showing. Remember, the hangtag itself is only a way to display your Pass, and is not valid for entry unless it holds a valid Pass.
If you own an open-topped vehicle (jeep, motorcycle, etc.) you may obtain a free decal to attach to your vehicle that will serve as proof of payment at sites that don't have a staffed entrance station.