Look on the bottom of the black control panel, where you turn the gas on and off. There is a sticker w/ the two letter date code, and also a full serial number.
I just want to share my excitement: I have been lurking here for a long time, but just last week scored 2 stainless steel Performers off of craigslist, to add to my original 2002.
For my birthday a few weeks ago, I rented a Ranch from the Weber Store in Palatine IL, and did 20 full slabs of babybacks on the RK for 6 hours, and 2 briskets for 13 hours on my Performer w/BBQguru.
Tonight I am doing a Corned beef brisket (experiment): it was mislabeled as a "pork loin rib half sliced" (I kid not) originally for $84.38, and marked all the way down to $10.xx! Also, 6 slabs, probably 2 Boston butts. Burgers and dogs for anyone who doesn't like the real 'q. Living here in "Feaux Cue" land everyone is really amazed by the real deal.