This brings back unpleasant memories and you would prefer not to dwell on it.
The Barcode Tattoo is a strange tattoo that has appeared printed on the arms of carapacians. Andrew's Formspring suggests that all carapacians with barcode tattoos were cloned.
The tattoo was first seen on the arm of the Wayward Vagabond, who refused to dwell on or explain the tattoo, saying it brought back "unpleasant memories". This may be a reference to his experiences on the Battlefield, or could be something unrelated. Spades Slick is the only character shown to find a use for them so far, when he discovers a barcode scanner in Lord English's vault. When he scans his arm, it opens a hatch to a base not unlike those which the Exiles encountered in 2422.
The tattoo resembles the unprototyped Battlefield.