Wiktionary
permanent dirt
n. 1 (context colloquial English) A tattoo 2 (context colloquial English) Any form of tattoo, piercing, (deliberate) scarring or other body modification that is considered permanent or would take significant effort to remove. 3 (context colloquial English) A hair dye or permanent wave that must be allowed to grow out or be reversed by repeating the process, that will not wash out.