Well, they are not legal and an MOT tester who is on the ball will fail the car. I believe that someone on here was pulled for having a Z logo, hmm maybe one of the mods/admin. Anyway logos outside of the following are not legal
Flags, symbols and identifiers
Flags and national identifying letters
You can display one of the following flags with identifying letters on the left-hand side of the number plate:
Union Flag
Cross of St George
Cross of St Andrew (also known as the Saltire)
Red Dragon of Wales
The letters, or national identifiers, you can have are:
GREAT BRITAIN, Great Britain or GB
UNITED KINGDOM, United Kingdom or UK
CYMRU, Cymru, CYM or Cym
ENGLAND, England, ENG, Eng
SCOTLAND, Scotland, SCO or Sco
WALES or Wales