I wouldnt consider a watch a defensive weapon... not unless you want to know exactly how long it takes the BG to die after hitting him several times in the lower abdomen with your handgun.
Seriously, I just wear a Timex Indiglo Expedition wrist watch with the leather band. Oh, and its the girls model... DONT LAUGH! I have small wrists! A mens watch is too big for me. I dont like big 'ol goddy things on my wrists!