The branding of criminals
Russian criminal tattoo encyclopaedia series by Sergei Vasiliev
During the 20th century in the Soviet Union there was a strong culture of tattoos being used to indicate one's criminal career and rank within Russian criminal and prison communities. Specifically for those imprisoned under the Gulag system of the Soviet era, the tattoos served to differentiate between who was an authority or thief in law, and who was a political prisoner.
The practice grew in the 1930s, peaking in the 1950s and declining in popularity in the 1970s and 1980s.