I just saw Monsters Ball a few nights ago and was struck that each of the 3 main characters - Halle, Billy Bob and Sean - had at least one tattoo. And in each case the tattoos seemed to match that character's personality.
Unfortunately they didn't do close-ups of any of them and none of the characters sat still with the tattoo visible so these pictures are on the fuzzy side. I did the best I could <img src="/images/graemlins/smile.gif" alt="" />
First, Halle. Of the 3, she's the one who you don't think HAS a tattoo. You only see it one time - it's on her butt and it's shown during the 'seduction scene' where she and Billy Bob are first together.
I think it's a manta ray or a similar shape - it's solid and fluid, sort of like her.