The great thing about custom number plates is that the car they are on does not even have to be worth anything to get attention from other road users. Often many old cars that sell are sold to people who really just want to take the number plates off and assign them to their car as their own. These combinations can only be removed if the person wanting them owns the vehicle themselves and applies to remove the registration plates. This is possible in some countries depending on the vehicles condition of being roadworthy prior to removing the desired registration. In the UK, it is possible to remove a registration from an old car however the car must have valid tax remaining and have a vehicle MOT.
Many old car owners who decide to sell their vehicles simply do not have an idea what their personalised registration plates could be worth. So instead of wasting any time, these classic cars which tend to be scrapped sooner or later, simply try selling the car they no longer can look after, to a potentially new owner who just wants to remove the number plates off the car and sell off any parts it may have.
Older vehicles tend to have the more desired shorter combinations attached which make out to read certain people's names, their nick names or a word they are looking out for. Being that these combinations are old, the ability of assigning them to most vehicles is possible as there is no real age restriction as most cars on the road are newer than the car which has the number plates on.
When a potential custom reg plate combination is assigned to an old car, and if you are the investor wanting the car simply because of the number plates it has, it is useful that you do not hint it out to the seller of your possible intentions of purchase and make them aware that they own a rust bag with hidden cash!