Played some Cthulhu over the weekend, and this idea came up.
Some practioners of the art don’t rely on books or scrolls, but etch their foul words on their very skin. Any caster may tattoo the a spell into their skin performing any checks as part of the spell then. The spell deals an additional 1d4 sanity damage and 1d2 hit points of damage in addition to its normal costs. The spell is maintained for a number of days equal to the bearers power divided by 10, rounded down. A caster may active a spell without it being an action on their turn but may only activate one per turn. When a spell is activated, it’s magic is used up, but the spell may be reinked to reactivate the magic. A spell may be learned from a magic tattoo even if the bearer isn’t alive.