The standard Virginia plate is LLL-NNNN. Non-standard plates vary from LL-NNNN to NNNN-LL. There are still a few ancient (circa 1976 ;)) plates around with NNN-NNN.
For passenger cars in Wisconsin, the current format (black text on white, 2002-present) is NNN-LLL. Before then, (red text on white, 1988?-2002) we used LLL-NNN. The old black text on yellow ‘cheese’ plates (pre-1988) were LL NNNN.
Passenger cars: LLLL NNN (older series: NNN LLL and LLL NNN, and, a long time ago, NNNNNN)
Graphic plates: <graphic logo>NNLLNN
Vanity plates: up to eight characters.
Commercial vehucles (trucks and buses): NNNNLL (older: LLNNNN)
Trailers: LNNNNN
Motorcycles: LNNNN
Plate colours:
Passenger: white with blue letters.
Commercial: white with black letters.
Diplomatic: red with white letters.
Dealer plates: yellow with black letters. I have seen one example of a dealer plate that was white with red letters. This must be new.
Motorcycle, scooter: white with blue letters, in a smaller size.
Moped: red with white letters. I think. It could have been diplomatic…
We had four numbers for a while, because the three letters (and long ago, two letters) indicated the county. The influx of people into the more populated counties caused the system to get out of control, so now the letters don’t stand for anything.
British plates: LLNN LLL (until recently LNNN LLL)
The arrangement is deliberate, in that a rhythmic alternation between letters and numbers is easier to memorise than a long string of digits.
In the new form, the first two letters designate the licensing region, and the numbers the six-month period of registration. In the old system, the first letter indicated a twelve-month period, and the last two letters the locality.
Idaho’s standard-issue plates use a number/letter combination to designate the county (1A is Ada County, where I live). 2A is Adams County, etc. For counties for which there is only one name starting with that letter, they simply use the letter (for example, Elmore County is designated by the letter E, no number). Following the county designator is the number, which can be anywhere from one to five digits. Once 99999 is reached, the first number becomes a letter (A1234, for example). Once Z9999 has been reached they go to two letters. Only Ada County, which is the most populous and thus has the most registered cars in it, has license plates with two letters followed by three numbers. If you’ve lived here awhile you can tell which counties in Idaho are more populous than others by noting how high the license plate numbers go.
Everything else in PA is LL-NNNNN such as trucks, trailers, farm equipment, municipal tags, state tags, and the plethora of vanity tags for every university and special group willing to pony up the $.
Years ago, South Carolina had alpha classing by vehicle weight, so every VW Beetle had a tag starting with A, a Chrysler Imperial would be perhaps a D, and so on. What that accomplished, I don’t know, but remember Dad explaining it.
New South Wales, Australia:
Standard: Traditionally LLL-NNN (black on yellow) until they finally ran out of combinations a year or two ago, and the new ones are LL-NN-LL.
Initial: LL-NNNN (white on black)
Custom: Any non-offensive combination of letters and numbers up to six characters (black on yellow).
Now, there are also slimline plates, custome coloured plates, “Euro style” plates. Very confusing. In general though, most Australian plates are LLL-NNN, and different states have different colour schemes.
Does this mean a maximum of 1,000 cars per county? Surely not!
I think Florida (where I currently live) is “LNN LNN”, but I’m sure there is more to it than that.
Back in the Western Cape, South Africa we still use the old Cape Province system: “Cx nnn-nnn” where x is one or two alpha characters indicating the district of registration. I think it can be liberally interpreted as corresponding to city size (“CA” being Cape Town and “CZ” being Beaufort West).