Well, why don't we make it a Campaign Equipment item, so everyone can buy / find it?
Names: When in doubt, keep it simple-
Tattoos - The normal kind, with 6+ save
Magic Tattoos - The Spell tattoos (a lame name, but that's what the Relics people called them, so no sense confusing people more.) Will grant a Lesser Magic spell, but for a +2 higher rarity roll, can be warband specific (ex. their own warband spell list OR based on alignment: good warbands can learn sigmar/lady prayers, taal, wood elf; evil warbands can learn Necromancy, Chaos Rituals, Dark Elf, or Blessings of Nurgle).
Warding Tattoos - The Dispel tattoos. What should they do, exactly? I'm thinking it grants a 4+ 'ignores the effects of an enemy spell that affects the tattooed individual' .On a natural roll of 6, the spell is COMPLETELY dispelled (otherwise, affects other models as normal. Cannot dispel spells that do not affect the warded model in any way.) Has no effect on Prayers. How's 100gc, Rare 10?