The Sierra Madre entertainer pass is a paper note in the Fallout: New Vegas add-on Dead Money.
Location
It is added to the Courier's Pip-Boy, along with the entertainer pass, after dealing with Dean Domino on the backstage stairs of the Tampico, at the end of Curtain Call at the Tampico.
Transcript
This appears to be a unique 'Entertainer Pass' for the Sierra Madre.