Ear

s are found on good characters (such as members of the Brotherhood of Steel or Regulators) when the PC has the Contract Killer perk. Daniel Littlehorn from Littlehorn & Associates, located at the Scrapyard, rewards you with 15 caps and bad karma for each ear, this is the bad Karma alternative to the Lawbringer perk(with Fingers instead of ears).

While you cannot kill essential characters, an ear will spawn in their inventory each time they are knocked unconscious. These can then be pick-pocketed from them, yielding an unending source of ears. How a person has an unlimited supply of ears remains a mystery.

If the player has bad karma, he will occasionally encounter a group of Regulators. These will yield as many ears as there were Regulators (usually 3), which can then be sold for 45 caps and bad karma. This can prove to be a good source of income if you have the patience. A good way to make Regulators appear is to fast travel to Metro Stations, which will usually cause them to spawn.

Trivia
The item itself may be a reference to the Vietnam War, where American troops would often sever the ears of Vietnamese soldiers as a post-death act of spite (the Vietnamese religion dictated that a man's spirit could only go to the afterlife if his body was whole).