At Federal recreation sites with entrance stations, you’ll simply show your card to the park ranger working the entrance stations.
But if you’re arriving to a site with no entrance station or there’s no staff member there to verify your pass, you’ll need to display your pass or show proof of pass ownership to compliance officers via one of the two following methods:
HANGTAGS — A valid national parks pass can either be displayed on your rearview mirror using a free hangtag or on your dashboard with the signature side showing.
DECALS — If you own an open-topped vehicle (jeep, motorcycle, etc.) you can obtain a free decal to display on your vehicle to serve as proof of payment