A well-known example is the Nazi practice of forcibly tattooing Nazi concentration camp inmates with identification numbers during The Holocaust as part of the Nazis' identification system, beginning in fall 1941. The Nazis' SS introduced the practice at Auschwitz concentration camp in order to identify the bodies of registered prisoners in the concentration camps. During registration, the Nazis would pierce the outlines of the serial-number digits onto the prisoners' arms. Of the Nazi concentration camps, only Auschwitz put tattoos on inmates.
The tattoo was the prisoner's camp number, sometimes with a special symbol added: some Jews had a triangle, and Romani had the letter "Z" (from German Zigeuner for "Gypsy"). In May 1944, the Jewish men received the letters "A" or "B" to indicate particular series of numbers. For unknown reasons, this number series for women never began again with the "B" series after they had reached the number limit of 20,000 for the "A" series. The practice continued until the last days of Auschwitz.
Tattoos were also used by sailor to be identified in case of wreck. After days floating in the water the face would often be unrecognizable and the tatoos would then help identify to body and be brought back to his relatives to have a proper burial. Tattoos have also been used for identification in other ways. As early as the Zhou, Chinese authorities would employ facial tattoos as a punishment for certain crimes or to mark prisoners or slaves. During the Roman Empire, Roman soldiers were required by law to have identifying tattoos on their hands in order to make desertion difficult.