Numbers. I once had a girlfriend with "mother with numbers". She lived in the house in Solna with several other Jewish families. All of them come to Sweden directly from the concentrations camps. Most of them had numbers and passed Auschwitz.
For some time ago I met my friend and I said, I remember Your mother and her numbers. She had numbers? My former girlfriend forgot about it because all people around her "had numbers". That was "normal"!
During the Holocaust, concentration camp prisoners received tattoos only at one location, the Auschwitz concentration camp. The site of the tattoo was the outer, later inner side of the left forearm. Tattooing was generally performed during registration when each prisoner was assigned a camp serial number.