They just seem to be prison system tattoos. It would be interesting to know if those numbers were unique for every prisoner across Germany or only unique within each prison because it might explain why it's difficult to find tattoos with numbers much greater than 1,000,000... however I haven't spent any time researching that beyond looking at hundreds of the tattoos.

They just seem to be prison system tattoos. It would be interesting to know if those numbers were unique for every prisoner across Germany or only unique within each prison because it might explain why it's difficult to find tattoos with numbers greater than 1,000,000... however I haven't spent any time researching that beyond looking at hundreds of the tattoos.