I dislike this recent trend (if it is one) of assholes stealing gear from artists (Noveller, Circuit des Yeux, now once again Thurston). Hopefully the guitar will be recovered, and soon. Some of the most wildest explorations of noise madness by Thurston have taken place with this guitar, I'm sure. It is for instance, the one he played when I saw him with Tom Surgal and William Winant in Mexico City a few years back. That show's burned in my mind.
Anyway, i think the serial number is: 41927, judging by a post by Eric Baecht, in case that information is not out there yet (I didn't check the Mustang site before posting this).