Prisoners from several transports in 1943 had their numbers tattooed on the inner side of their left upper forearms. Tattooing was generally performed during registration when each prisoner was assigned a camp serial number. Since prisoners sent directly to the gas chambers were never issued numbers, they were never tattooed.
Prisoners received tattoos only at one location, the Auschwitz concentration camp complex.
https://encyclopedia.ushmm.org/content/en/article/tattoos-and-numbers-the-system-of-identifying-prisoners-at-auschwitz
Prisoners from several transports in 1943 had their numbers tattooed on the inner side of their left upper forearms. Tattooing was generally performed during registration when each prisoner was assigned a camp serial number. Since prisoners sent directly to the gas chambers were never issued numbers, they were never tattooed.