This is Olivia's tattoo.
It's forty-two in roman numerals (they looked prettier). If you've read The Hitchhiker's Guide to the Galaxy, you'll get it. If not, its the answer to the ultimate question of life the universe and everything.
I love when people ask me what my tattoo is because I just get to be a big geek and say, oh you, know just the answer to life, and giggle to myself at their inability to understand.
"For instance, a race of hyperintelligent pan-dimensional beings once built themselves a gigantic supercomputer called Deep Thought to calculate once and for all the Answer to the Ultimate Question of Life, the Universe, and Everything.
For seven and a half million years, Deep Thought computed and calculated, and in the end announced that the answer was in fact Forty-two --- and so another, even bigger, computer had to be built to find out what the actual question was."