No cite online, but Ripley’s Believe It or Not! once featured a Leo Lee, who requested (and got) license plate 337 037 - and put it on upside down.
NOHFRS
On a pickup with a young male driver. I hope he ends up with a fat wife and 6 kids.
(“No Heifers” which is a western way of saying, “No fat chicks.”)
There were two I saw a few months back that had me puzzled, but for different reasons.
POSN OAK - what I couldn’t figure out was, why would someone want Poison Oak?
PI KNOTR - I actually, finally, figured this one out today, after months of trying to figure out how you ties knots in pies, or maybe they were talking about knotty pine … (at least, I think I figured it out)
I have a long, long list of license plates that have amused me over the years. One I saw in VA, on a pickup truck, read CW TIPPN. If I ever find the list, I might post some more.
Seen on a Honda Element in Los Angeles:
DRZAIUS
With bonus vinyl stickers of who else? But Troy McClure as Dr. Zaius 
Framed with a Simpsons license plate frame.
ETA: just remembered one lady I saw on the 405 daily in a Benz with the plate 1199ESQ. Made me wonder if she actually got out of tickets or if CHP went out of their way to nail her.
A car in my neighborhood has “BALZBUB.” I always wonder who they had to know to get that one by.
Actually it probably stood for “Ciao Tutti”, which means (approximately) “Hi, y’all”.
Someone who used to live in our old neighborhood had a Porsche that read
CUZICUD ("'cause I could").
I also once saw a sporty red car that said:
FZMGNT (“Fuzz Magnet”).
And I saw a convertible that read
“OBN OHNE”.
Which meant absolutely nothing to me… but my passenger at the time spoke German, and she explained it was “Oben Ohne” (sp?), which means “topless”.
There’s a green Bug around here with plate KURMIT. Kermit must be taken.
I prefer the one I’ve seen: ACTULSZ.
Oh, I like that one!
Here’s what I would like to see:
4NIC8 or 4NIC8R
I doubt most states would let these pass.
And for us Dopers…
AUNAFPD
14K (gold=Au) in a F P D
Hate to quote myself, but I’ve decided I didn’t figure it out. I thought it was from the bit about “PI R Not Square, PI R Round”. Except if it is, it’s saying that “PI not round”, and that doesn’t make sense.
So now I’m back to wondering what it means. Ideas?
Someone near where I used to live in Chiago had a license plate that read:
WE DO 26.2
The dot was obviously added to the official plate. It took me a while to figure out that the owners must have been marathon runners.
- Isn’t k the usual variable for a constant?
- Pi Kappa=?
It could almost be pinot noir but the k would be a waste.
O HAI, by the guy who runs catster and dogster.
I’ve posted this before, but I saw:
GRR ARGH
If it’s a variable, it is by definition not a constant. 
Mentioned in today’s paper is a Fit with the plate
HISSSY
Oo! Just thought of a couple more I’d heard of (but not personally seen):
On a white Volkswagen Rabbit: IML8
On a black Volkswagen Rabbit: ENLI
And, lobotomyboy63, I don’t think so about the k. My (dim) recollection from algebra is that the letters a-m were traditionally used for unknown constants and n-z were used for variables. Besides, it doesn’t help in the interpretation.
I’ve seen a white Rabbit with the plate
ML8ML8. It took me a while, but I figured it out. The one I saw was from New Hampshire, but I gather from this Board that there’s at least one state with the same plate out there. Probably more than one.
A friend told me about seeing a Black Rabbit with the plate INLE (nitpick: not ENLI), referring to The Black Rabbit of Inle from Richard Adams’ “Watership Down”). I’ve never seen it myself.
You see, this is what happens when you don’t have the thing written down somewhere, and the book is packed away in boxes. You are, of course, right. :o