Acquiring enchanted Body Art seems like a fantastic opportunity for Foreground Growth or Improvements to a Character obtained in Play. I imagine quite a bit of Adventuring might be required to locate the highly specialized Arcane Artists who can preform this delicate work. Charging steep Prices or only deigning to design one as a reward for Services Rendered. The Process could potentially also involve some sourcing of unusual or difficult or dangerous to acquire Reagents/Ingredients for use in the Pigments or as Needles. The resulting piece is likely brilliant to behold in terms of craftsmanship but these can also impart Magical Gifts to those whose skin they stain. I’ve always been a fan of granting Classes a little bit of limited Spell-Casting or Unconventional Abilities this way, and this kind of non-item-based Magical Augmentation can’t be as easily Removed via Ravenous Rust Monster.
How would these Magic Tattoos work in Play? My current line of thinking is to use them in conjunction with a Usage Die Mechanic (since the energy contained within them is less quantifiable), perhaps set it starting at d8, d6 (or even d4 for some of the more powerful ones, or more generous for the less), on each “Use” or “Activation” there’s a chance (on a roll of 1 or 2) the Incantations embedded alongside the Ink might begin to fade or become lose potency. Once the Magic depletes completely, the Tattoo vanishes! I’d recommend the Restriction that one set of Skin can never receive the same Tattoo Twice, in order to keep these a little more unique and special.
Here are a Hundred Ideas for these, along with some suggestions for “Flash” or descriptive designs.