In the UK all license plates for cars are issued from one central authority. Here in the US, each state issues its own plates. Each state plate is different, not only in having the state name but in colour, font used, and numbering pattern.
The standard California plate has a white background with a seven character mix of letters and numbers in blue. (I know they look black in this picture, but they are really blue)

I say standard, because for an extra cost, you can have a different background. Part of this extra cost goes to an environmental or educational fund depending on the plate chosen. Moreover, for a fee you can have any unused choice of characters. These characters can include hearts, starts, spaces, or a half space. A half space allows you to have the full seven characters with a gap, as I saw on a plate declaring the owner to be GEEK GOD. The heart is obviously used to state love, often between two sets of initials; the California equivalent of those green windscreen stickers with a pair of names, which I associate with drivers of Ford Capris. Details of the custom numbering scheme and backgrounds are on the Department of Motor Vehicles website.
Many states also have a slogan on their plates, usually beneath the number. This may be the official state nickname such as New Jersey’s “Garden State” and Missouri’s “Show Me State”. In the case of Idaho it describes that states major export “Famous Potatoes”. The state of Michigan uses this blog’s title, or did, I am not sure if the steady decline in sales of Detroit made cars has forced a rethink. New Hampshire has the slightly bizarre “Live Free or Die”. A full set of plates can be seen at this site, but the pictures are several years old and some may have changed.