Last year North Carolina officials made fools of themselves trying to withdraw licence plates containing the letters WTF while having posted the very same letters on their official web site. Three letters if put in that particular order may be read by computer literates as What The F$%k? In order to avoid some people being offended the NC government put hold on use of that abbreviation.
The Government of the Province of Quebec while refusing to issue personalized plates to its drivers, maintains ignorance to the computer lingo and randomly issues WTF plates:
Please have a look at the STFU plates from Arizona and Virginia - they seem to be perfectly legal.