Pass Card

In Fallout 3, s are items that are randomly encountered.

Locations:
Pass cards are located in random places throughout the Capital Wasteland. They are dropped by ghouls or centaurs, and may also be found on trogs if The Pitt is installed.

A ghoul has a 1 in 80 percent chance of dropping a pass card of either color, A centaur has a chance of about 1 in 170, & trogs have an even smaller chance of about 1 in 240.

Notes:
The cards seem to have no purpose. (they are not accepted by Protectrons in lieu of metro tickets!)

Trivia
They could be a reference to the area from Fallout 1 called The Glow. You needed red, blue, and yellow pass cards to move to the lower levels, or its an homage to Fallout 2, where you needed red and blue pass cards to move around a ghoul run nuke plant.