In prison, tattoos represent self-identification and belonging. To those who have them, they represent the rejection of straight society and membership in the outlaw class. Marked goes deep into the culture of prison tattoos, discovering how these illegal marks are secretly created behind bars, and decoding the meaning of the strange symbols that cover many prisoners' bodies. We explore the secrets behind the marks through the experiences of current and former prisoners, and examine the bloody ways that these initiation marks are earned.