Some of these tattoos look like they've been designed based on some real life prison tattoos.> Skulls on knees
Russian criminals used to tattoo stars on their knees to represent "never kneels to police" - the tattoo went out of fashion when guards began having fun purposefully making every inmate with such tattoos kneel.> Roaring bear
A roaring beast or devil is tattooed in Russian prisons with the same meaning.> Castle
Substitute it by church, and that's how the tattoo is used in Russian prisons, except the number of domes represents not years, but number of prison terms.> Finger ring tattoos
Also used in Russian prisons and have quite a lot of meanings depending on design of the ring> Web
I heard that in American prisons the tattoo is used in a similar meaning. Not sure if it's true.