Stained note is a paper note in the Fallout: New Vegas add-on Dead Money.
Location
On a desk in a second-floor room in the far northeast corner of Puesta del Sol North, accessible only through a broken hole in the wall above a courtyard filled with The Cloud (the Cloud may have been cleared if the player has reactivated Puesta del Sol's ventilation systems at the Puesta del Sol switching station already).
Transcript
Liquor shipment finally came in today - didn't realize working here would be like working in a dry state. Just need to keep it out of sight of security and Sinclair, and ought to take the edge off the day, keep it stashed in the back.