I suspect the GP was referring to this: https://encyclopedia.ushmm.org/content/en/article/tattoos-and-numbers-the-system-of-identifying-prisoners-at-auschwitz h

I suspect the GP was referring to this: https://encyclopedia.ushmm.org/content/en/article/tattoos-and-numbers-the-system-of-identifying-prisoners-at-auschwitz https://encyclopedia.ushmm.org/content/en/article/tattoos-an...