GMCer...These are personalized plates you order from CA DMV. There are a few background patterns you could choose from. YOu could just order the background with standard Lic number or personalize it like I have.
John... go to the DMV website, pic your pattern then you could add your lettering/numbers/spaces and you could view what the plate looks like with the background and custom lettering. YOu could create it, order it and pay for it online. I must warn you though that when you call DMV to ask why it's taken almost a couple of months, they're response would be, it could take up to 6 months. No refunds also! Try this link:
http://www.dmv.ca.gov/online/elp/elp.htm and just scroll down to see the special interest plate styles.
Also, when you purchase these plates, you own them. After they arrive, they will notify you and you could assign them to any vehicle you choose by taking your old plates to DMV when you pick them up. It would be wiser to personalize them to something other than a vehicle description, so that if you sell that vehicle, you could keep the plates and designate them to another vehicle. I figured if I want to put them on a non-GMC, I could always say it means General Manager of the SEA, LOL