The note can be found in the Sierra Madre casino on the counter of the dining room on the 2nd floor, next to three Sierra Madre chips. Unlocks the [Hard] locked security management control terminal upstairs in the casino's security room.
The passcode for the cashier room security hologram is "MrFizzle17." Please don't forget it again, I could lose my job if they found out I gave it to you. See you in the electrical closet after the Gala Event?