Here is my Ironman tattoo. It may take you a minute to see the 140.6
I love it. Check out my Pre Ironman post for the story behind the Octopus. The short joke I've been using is that I am a lot like an octopus; I'm a good swimmer, I run slow in land, and I look silly on a bike. If you want to beat an analogy to death, octopodes are also smart, have long arms, and often try to go unnoticed (camouflage).
As far as the tattoo goes, I also love that's it isn't terribly obvious that it's Ironman. You don't notice the 140.6 in the arms right away, but once you see it you can't see anything else. It's awesome.