The new Futurama straight-to-DVD movie (coming out soon) features a plot relying heavily on a tattoo of Bender (robot) that Fry (main character) unknowingly has on his butt.

The plot mirrors a 'Back to the Future' story line. 'Within' the tattoo, is binary code which possesses the unique key for time travel, which is used throughout the movie.

http://en.wikipedia.org/wiki/Futurama:_Bender%27s_Big_Score