THE Tattoo

Each of the 9 actors in the Fellowship got this tattoo somewhere on there body. It's the elvish number for 9.

An excerpt from There and Back Again, An Actors Tale by Sean Astin:
"Orlando was tattooed on the right forearm, Viggo and Dom on the shoulder, Elijah on the lower part of his belly, near the hipbone, and Bret on the small of his back."
(Bret being John's scale double.) He also mentions Ian getting his on his right shoulder and Him and Billy getting it done on their ankles.

Picture from theonering.net