Pass Card

In Fallout 3, s are items that are randomly dropped by ghouls or centaurs.

There is no place where a pass card is guaranteed to be found. A ghoul has a 1 in 80 chance of dropping a pass of either color; for a centaur the chance is about 1 in 170. The cards have no purpose: they are not accepted by Protectrons in lieu of metro tickets. During the Pitt, some of these cards may be found on Trogs.

Trivia
The presence of these items in Fallout 3 may be a nod to the preceding games in the series as Fallout and Fallout 2 featured Red, Blue, and Yellow Pass Keys which were used to open corresponding doors, it could also be a reference to DooM, where Red, Yellow, and Blue passkeys were required to advance in the levels.