The National Park Service has a program where Junior Rangers can collect…

A Badges
B Stamps
C Coins

There are over 200 Junior Ranger programs at National Park Service locations. Visitors can request Junior Ranger handbooks, complete the activities inside and return to the visitor center for a badge or patch at most parks. The program is designed for children, but all ages can participate, so no frowns, kids-at-heart and park ranger wannabes.

The correct answer is Badges.