(Photo from Rocksubculture)
Update: He's also had a "Come Along Pond" sticker on his white bass, and also wrote that on his arm.
(Thanks Charlotte Sometimes)
Update (10/21/13): Yet another Doctor Who reference from Simon, and further proof of his awesomeness. See those sets of marks on his arm? He must have run into The Silence quite a few times in Austin! ;) Thanks to Rev. Heron for sending the photo, and to Fuji for taking it at Austin City Limits on Oct. 5th.
Update (03/31/14): And his latest Who sticker, A Good Man Goes To War, was displayed at the Royal Albert Hall shows on March 28th & 29th, 2014. Thanks to Perfect.Murder for spotting it, and to Olivier at It's A Perfect Day for the photo.
Update (5/30/14): No change at the BottleRock show. Still has A Good Man Goes To War sticker.
This is really fun! Have there been any other DW stickers or markings that I've missed?