From the GM site:
The first 25 SSRs produced will be coming in early 2003 as the Signature Series. These vehicles will be identical in appearance and have certain features not found on any other 2003 model year SSR. Things like ultraviolet paint, unique badging, and special interior. These SSRs will also be used in a variety of high-profile activities around the country leading up to and following the start of regular production. Ultimately, all of the Signature Series SSRs (with the exception of vehicle identification number #1) will be offered for sale at various types of auctions during 2003.