They're all highly appropriate! They all mark the owner down as complete wafter who believes in their own legend and perceived importance.
My neighbor has RA08 RTA and her name is Roberta, so it's highly appropriate that such a desperate stretch for imagined glory marks her down as the total wally that she is. Her son also has (I'm guessing) his initials on his vanity plate H7 HTB, so stupidity breeds stupidity, clearly.
Private plate = Desperate social climber. With very, very few exceptions.
Be interesting to know what you spend your disposable on.