Tattoos, as mentioned in Professor Martin’s Fenians in the Frame, were the most reliable forms of identifying wanted people/prisoners. Seamen, and working men, also were generally heavily tattooed as well. I learned, through a quick google search, that the first tattoo machine was invented during the Victorian Era, and supposedly little alterations have occurred. Tattoos, especially during the Victorian Era, were quite popular.
Tattoos were also pretty prevalent amongst royalty, but were kept incognito….