German number plates :the first 1-3 letters:
The district/where you live.
after a free space : if you pay an amount of ca. 10 euros you can order one or two letters (if they are free)
the numbers (1-4 digits,third part of the id) are able to order as well.If you don`t pay,you`ll get a random one.

In Great Britain each CAR has its own number plate id.There's a market for cool number plates in the news papers.The last letter expresses the year of first registration.
(maybe the rules changed meanwhile ,info from 30 years ago)

In Austria the PERSONS do have a car id,which changes to the next car.no idea what happens if you got more than one car.

How is that in US and in other countries?

There is no "National" standard except for size and reflectivity in the U.S. Each state has their own rules. About the only thing you can't put on a license plate is mean, dirty, or harmful remarks or statements.

In Alabama, as far as standard plates go, the lead number represents the county you're in. There is a a cycle that generates the second digit in letter based on the month you get the tag. After that, numbers are randomly generated by a system that checks to ensure no two plates match. I'm not sure at what point a specific combination is allowed back into circulation after it's expired.

Here you have what you get

Plus the number plates tell from what
year a car is

I had found this link when I was researching to buy my plate from Germany:

http://de.wikipedia.org/wiki/Liste_der_Kfz-Kennzeichen_in_Deutschland

There's a lot of information there.

In Cali, there are different color plates & designs for like every 20 years,etc. Standard plate differ from trucks to SUVS, Passenger cars, to Motorcycle & Semi Tractor trailors. Pass. cars & SUVs have 3 letters within the plate eg; 1"ABC"234, Pickup Trucks, 1 letter 1"A"2345, and other variations for easy spotting if someone tries to swap plate from their boat trailer to avoid paying reg. fees for the vehicle. There are specialized "Vanity" plates too like mine. There is a panel of people you submit you request to for certain vanity plates. Nothing offense, vulgar,etc. As in MY case. They would not allow any plates that states "IMA COP", "THE FUZZ",etc.. I had to spell it "THAFUZZ" to get around it. Silly cause it still sounds the same darn way when you read it anyway. So, there's MY story on
THAFUZZ plates. Other states will add a Smaller set of letters within the plate for your county or region within an individual state. Hope this much helps.

Here are the number plates from Holland

Car/lorrie

Motorcycle:

Taxi:

Moped 45kmh

moped 25 kmh: