You're kidding! No? You turn the fingers in at the Regulator HQ to Sonora Cruz. Second Floor. Its also in your notes section. Regulator HQ is a house in the Capital Wasteland and the headquarters of the Regulators. It is the farm house located north of Wheaton Armory and west of Canterbury Commons. This location is given to you once you add the Lawbringer perk to your character.
Outside of the house are three brahmins, and inside are three Regulators. Sonora Cruz should be outside tending to the cattle, she may also be inside. It is entirely possible that she is no where to be found and you will have to go looking for her. his location is given to you once you add the Lawbringer perk to your Character. For each evil person (Raider, Talon Company, Etc.) you kill you will see a finger in their inventory. Bring the finger(s) here to trade in and receive good Karma and caps.