What? 
You just read the characters out loud:
4 = for
BN = bein’
GD = good
I saw one that read “PLN 6 GS”
The only thing I could think of is “pulling 6 g’s, as in G-force”. As it was not on a very expensive car it probably wasn’t a reference to income, or rocketry. Plus, I’m not in rocket land. And the model of the car was not a GS of anything.
Are astronauts subject to 6 G’s even?
Make that PULN 6 GS.
It is pretty lame
for bee en gee dee
I’m not saying it isn’t kind of a lame plate, just that it doesn’t require any sort of culture-specific code cracking. 
My brother and I noticed this one when we were kids, and I still think it’s the coolest plate I’ve ever seen:
APOXONU
I’ll take a stab at it:
Decipher this?
Did I get it right, Misnomer?
Uncommon Sense: Maybe he was bragging about making six grand a year?
About 20 years ago in State College PA I saw ANSR42
D’oh!