Since 1945 Idahoans could tell where most cars are registered simply by looking at their license plates. It’s handy if you want to grouse about the “Great State of Ada,” or that BMW from Sun Valley, or that clueless driver yet to find his or her turn signal switch from, say, Canyon County (just to pick one at random).
The way it works, in case you just moved here from California (to pick a state at random), is that the letter stands for the first letter in the county, and the number refers to where that county would rank in an alphabetical list. For instance, 1B is from Bannock County and 2B is from Bear Lake County.
Learning the county designators, and thus the counties has been a great game for road-weary kids for generations. Then, along came personalized and specialty plates. Neither carries a county designator, so if you want to go incognito you can get a personalized plate such as GOFISH. It’ll cost you a little extra. Also, you could show your affinity for some activity, group, or whatever by getting a specialty plate.
Legislators have mucked around with limits on how many kinds of specialty plates are allowed several times. They seem to have given up on limits nowadays if you can find enough friends who also want a plate that shows their affinity for horned toads or counted cross-stitch. The plates must sell X number a year (also a moving target in any given legislative year) for two years. The last time I checked there were more than 70 specialty plates available. If you want your specialty Corvette plate to read 2RICH, you can do that. Specialty plates can have a personal message.