If your car was used, I would think that your plates are actually behind the dealer "plate." I had a used car before that had the plates right behind the dealer logo. The reason that the dmv hasn't sent you anything is because your tags haven't expired. Go out to your car and feel for the plate behind the dealer "plate." You'll see, that way you can take off the dealer's advertising.

By the way, Nice job on the spoiler delete. It looks awsome!