Custom license plates are a great gift idea. On designasign.com you could create Custom license plates or vanity plates for anything you like. In the states that you do not need state registered plate on the front of your vehicle the plate could go in the license plate area. Even if you cannot use a personalized license plate on your vehicle there are a lot of different place someone could put a custom license plate.
Kids and teenagers might put a personalized license plate in their room with their name on it or their favorite sports team. You might see custom license plates in a bar or game room. This is a great novelty gift for a couple that just got married. They could have their names on it with maybe a picture of them with their date printed directly on to the personalized license plate.
A business owner could give these away as novelty gifts with their customers with the companies name and information on the license plate or just advertise on there own vehicle with a custom license plate.
Personalized license plates are great as novelty gifts at social events. A custom license plate for a favor at a bar or bat mitzvah. Give one personalized license plate out to every kid with their name and the guest of honors name on the custom license plate. You could do the same thing for a corporate function. Giving out favors as custom license plate to all the guests.