Trying to figure out just what a mathematical anomaly is is like driving two flats crossing the border to Mexico: I’m out of ideas.
If you just mean cool mathematical stuff, I can throw some stuff out there.
One of my favorite mathematical formulas is that for the function of a normal distribution. [Link.](http://mathworld.wolfram.com/images/equations/NormalDistribution/equation1. gif) It’s just so simple and pretty and describes something so common and profound in statistics.
Another simple and profound thing you could forever etch into your body could be something to do with Boolean algebra, like maybe a Hasse diagram.
Oh, and have you considered a fractal? That would be nerdy, Woodstocky, and awesomey.
Box fractal - Almost doubles as a neonazi symbol
And for the super pretty, a star fractal.
Something from topology would also be fairly hot. Unfortunatly, I’m a total topology noob, so maybe someone else could point you to something good there. I was trying to find something on a Calabi Yau space or a Hodge diamond, but couldn’t find anything worthwhile.