Customized license plates are the license plates on cars that have a message in them. Usually letters and numbers are placed on the license plate and they have some sort of meaning to them. It may be an expression or a phrase or even a word are two that is about the driver. Customized license plates were popular at one time but it seems that not as many people get these license plates now.
They do cost extra. Instead of getting a regular license plate sometimes people will get a license plate that has a word or phrase on it that means something important to them. However I do think that it is lame to get customized license plates because you can get a bumper sticker and it has the same effect.