What do the numbers on the Autobots license plates signify?
They correspond to the numerical designations of the Car Robots toys. The original version of Speedbreaker (Sideburn) was C-004, but Super Speedbreaker was C-026 (which is why he changes license plates on the show when he powers up). The reason there are no characters with the designation C-011, C-015, or C-022 is because these were the numbers attributed given to the Spychangers giftset, the JRX (Rail Racer) giftset, and the Build King (Landfill) gift set, respectively.