Take a close look at the recent media coverage of the rioting in France, and you will see that those young French men of Arab and African descent are wearing identifying tattoos.
In England, law enforcement officers often find the letters "ACAB" tattooed on hardcore British criminal gang members. The cops in the United Kingdom say this stands for, "All Cops Are Bastards." However, if you ask a person who wears the ACAB tattoo, he will say it stands for "Always Carry A Bible."
The Russian criminal gangs have developed a very complex and elaborate system of recognized signs and symbols used in the Gulags since the 1920s. I have seen many booklets, photos, and briefings on Russian criminal tattoos.
However, like the Cuban Mariel criminal tattoo information, the only sources of the information are often the foreign criminals themselves. This causes some of the available information to be less than accurate or even incorrect.
In general, the Russian gangs are divided into criminal specialties. The four suits of playing cards symbolize the primary specialties. Spades, especially when depicted upside down, are considered "the suit of thieves." Clubs are "the suit of criminals." Diamonds represent "the chummy suit" of criminal slaves and servants or government informers. Hearts are a sexual symbol used to mark the wearer as a "passive homosexual" or a convicted rapist.
In the Russian underworld, skulls symbolize high rank or extreme violence. Crowns and epaulettes are also symbols that are often on Russian gang leaders.
I would recommend that if you have a particular interest in Russian criminal tattooing systems that you attempt to find the 70-page booklet "Russian Criminal/Prison Tattoos" published by the Canadian Embassy in Moscow last year. It was compiled by Graham MacCaffrey with Natalina Senatorova, and it is an excellent reference manual to Russian criminal tattoos.