A vanity plate or personalized plate (U.S.), prestige plate, private number plate, or personalised registration (UK) or custom plate or personalised plate (Australia and New Zealand) is a special type of vehicle registration plate on an automobile or other vehicle. The owner of the vehicle will have paid extra money to have his or her own choice of numbers or letters, usually forming a recognizable phrase, slogan, or abbreviation on their plate.
In the United Kingdom, number plates are issued by the Driver and Vehicle Licensing Agency (DVLA). They do not approve personalized registrations if they contain words which are offensive in any widely used language. The DVLA however lately have released more and more previously banned combinations such as SEX and DAM.
There is some additional flexibility available by using numbers that resemble letters (e.g., S for 5), or by using large black, yellow or white headed screws to fix the plate to the car to fill in or create a gap (e.g. in the middle of 'H' to make it look like two 1's or I's). However, the font style, size and spacing is mandated by law, making the practice illegal.

en.wikipedia.org/wiki/Vanity_plate