Rob writes in:

This is the symbol from the front of the Doctor’s fob watch, seen in the “Human Nature” and “Family of Blood” episodes of Doctor Who. Since this watch was directly involved with the Doctor’s transformation (Gallifreyan – Human) I thought it was appropriate since I transformed myself last year by losing 100 lbs!

The tattoo was done by the excellent Tom Sardinha at Shogun Tattoo in Salem, NH.