User becomes stronger, faster, more durable, etc. when they are near, come in contact with, or have tattoos, possibly to unlock abilities related to what the tattoo is based on and enhancing their existing powers. Some users may be able to draw sustenance from tattoos or even slow or stop aging.
Esdeath (Akame ga Kill!) gained a tattoo on her chest after ingesting the Demon's Extract which served as a catalyst...
...to unleash deadly and powerful ice based powers.
Mark Richards (DC Comics), the 3rd Tattoo Man.
Abel Tarrant (DC Comics)
Pix (DC Comics)
As the Zombie Tattoo rapidly spread on Alviss (Marchen Awakens Romance) he entered a brainwashed state where his magical power increased tenfold.
Tattooed Man (Marvel Comics)
Ryoga Hibiki (Ranma 1/2) with the Mark of the Battle God tattoo that not only improves his already near-supernatural strength to absolute strength levels but reduces all damage done to him to the equivalent of a feather falling on him
With elements of a pentagram, or endless knot, Anti-Demon Possession Tattoos (Supernatural) can ward off demonic possession...
...due to these tattoos, Sam and Dean Winchester are immune to any and all forms of demonic possession.
Demon Slayers (Kimetsu no Yaiba) such as Kamado Tanjirou who have unlocked their Mark gain an increase in their already remarkable physical abilities and achieve the ability to utilize See-Through World….
…Yoriichi Tsugikuni was the first to unlock the mark from birth and he lived to be 85 years old despite it supposedly killing the wearer at 25 years old if overused.