The uk has a whole industry in buying and selling 'cherished number plates. Its easy to transfer them to another car, unless its an age related plate (the current plates are '72') that makes an older car look newer than it really is. But you could fit a 71 plate to a 72 plate car if you want.
And some people keep their own personal plate for years and transfer it to their next car. Maybe their initials, or they just like it.
Number plates from very old cars with few letters and numbers, especially someone initials can sell for many thousands . Its estimated that the UK number plate A1 could sell for £10 million
But regarded as an investment -maybe next year it would sell for £11 million.
Also popular are number plates that appear to read a word. such as Comic. (COM 1 C ) Some people try to make a number plate read like a word by using bolts in the wrong place etc. Its illegal, but they still do it.
Our own DVLA (Driver and vehicle licencing agency ) have got in on the act. They wont issue any that look good and sell them them for silly money. Often they auction them to the highest bidder They also refuse to issue any that apear to read as something rude.