Rune tattoos would provide combat statistics and even some magic, I would like to have one that would warn me or attract something supernatural, something comes close to the mark of sacrifice in Guts from Berserk, because of getting the false god slayer!
Oh, I made a theme - a collection of ideas. In short, tattoos would serve as an additional weapon for a magician. In case of slavery, and even that which cannot be lost. (Something like what's in Fullmetal Alchemist)
