A tattoo describes the design obtained where ink is injected by a needle below the surface of the skin. It is, for all intents, permanent, although it can be removed at great expense and discomfort to the patient.
Eric Foreman has a tattoo on his left wrist that he obtained when he was in a gang as a teenager. He tells people that it is an oriental design.
In Acceptance, the metallic inks in the patient's prison tattoo cause him great pain when he is subjected to the magnetic field in the MRI.