Although I am not a tattoo wearer myself, I can appreciate the intricate patterns and symmetry that many such artists bring to the canvas of people's skin. My preferred medium, fractal art, shares a lot of the same principles -- the tattoo artist does literally by hand what Apophysis 2.09 and other related programs do digitally to create art of magnificent detail.
If I were to have a tattoo, I'd choose among my own wild heart fractal art pieces. My skin is golden brown, so I had to think about what color ink would blend well on that -- and, above, voila!