No, I seem to be the only one who noticed what I guess is an innocent typo in his post:
He has E20, when everyone has since admitted it’s E23.
You still haven’t convinced me that you’re right. 6.022 * 10[sup]23[/sup] = 6022 * 10[sup]20[/sup] Since you can’t have a decimal point in your plate (unless you paint one), only the latter can be accurately printed on a plate.
If you wanted to be less precise, you could say 6E23. But if you add a digit to be more precise, you’d have to adjust your exponent and say 60E22. Since you obviously want the familiar-to-most 4 sig figs, 6022E20 is the mathematically correct option. Without a decimal point, that’s the only way to make it the right number.
Now, granted, if I saw the technically incorrect 6022E23 on a plate, I’d still get the chemistry joke. But, at the same time, I’d probably think back on it later and say “What a minute…the scientific notation is wrong!”
Oh.
I honestly didn’t understand that you were accounting for the moved decimal. I thought the decimal was so implied and understood that it didn’t occur to me.
I passed a Stoofes fan (I assume) this morning, with the plate:
**HEY MOE**
…
So you’re painting a decimal on your plate, then? 
I think it’d look cooler, anyway. You can get a small bottle of acrylic for $100 (umm, $1.00 ;))
(Sorry for the hijack, but I think it’s a cool plate. It’d be even cooler modified, though.)
Or a blue sticker. I have a feeling that it might be some illegal alteration of the plate. I actually got a fix-it ticket once for having a clear plastic cover over my front plate. I’d bought the car with that, and it had been there for 8 years, but some cop was bored, and decided to pad his numbers with it. A sticker would be easier to fix.
Today I saw REDROVR on a maroon Land Rover.
A gentleman who would often be on the freeway at the same time I was had a white Bronco. His license plate:
NOT OJs
A couple weeks ago, I passed an RV pulling a mini. As I came Up to the mini, I saw its plate was IPUSHRV. When I got up to the RV, I could see that its plate was IPULMINI. Made me laugh all the way to class.
Cardinal, I do think it’s assuming a lot to assume every Doper knows not only Avogadro’s number, but also the “E” notation for it. It’s been quite a few years since scientific literacy could be taken for granted here on the intertoobz.
British registration plates don’t lend themselves so well to this, as they can only use certain patterns of letters and numbers. However, this morning I did see a cement truck with the plate M11 XOR.
How leet is that?
When I was a lad you could still get things like “JIM 1” from the DVLA. Do they not allow that anymore?
When I lived in New Hampshire, I was near the Vermont border when I saw a car with the Vermont plate “KVELL”, followed by a (undoubtedly related) pickup truck with the Vermont plate “SCHLEP”.
There was an older guy at my previous church with PAC POW on his plate. He also had a sticker of “Wake Island Defender”. A few years ago I realized I hadn’t seen that car in a good while. That whole generation is dying off 
Puttering down I-66 towards DC, I was passed by a Ford GT with this Virgina plate:
0-60 3 3
(Can’t remember if there was a . in between the 3’s)
<< Insert witty sig line here. >>
I rode my motorcycle for about 6 hours on the highway this weekend, and saw a few gems:
MYSKIHI on a Saturn Sky
JALPNO on a dark green Mini that actually looked kind of like a jalapeno
and, perhaps my favorite, an older Land Rover that had
GIT R as the license plate, with stencil-type stickers underneath that said
DONE
Alternate suggestion for GT owners: 14 MPG
Yes - that is an example of one of the “certain combinations” I mentioned. Basically, in the old days they started with A1 and eventually went up to combinations of three letters and up to three (or possibly four) numbers. So you could have JIM 1 or 123 SUE.
Then in the 1960s they switched to a suffix letter that indicated the year, so you’d have three letters, then a number (between 1 and 3 digits), then the year letter, which was only issued in that year. So you’d have stuff like TDH 427G, and you got what you were given. You could buy numbers that appeared to spell words, but you’d have to be creative - they still had to fit the pattern: COM 1C when the year letter was C, PWN 3D the following year when it was D (assuming you had a premonition about internet slang in the 1960s, of course!).
When they ran out of year letters, they switched the order so it was year letter - 1-3 numbers - three letters, e.g. A643 GYJ. Again, if you wanted a personal plate you’d have to be creative: K15 SME pr P155 OFF, perhaps (I’m sure they wouldn’t have allowed this one!).
Then, a few years ago, they ran out of letters again, and switched to the current system, which is even less conducive to spelling out words: two letters, which are related to the area the car was registered, then two numbers, which relate to the year, then three letters, e.g. LD08 JTW. The two numbers are always either the year digits or the year digits plus 50 (for the second period of any given year), so this year you get 08, or 58 after September. There aren’t a whole lot of ways to spell out words this way, although some plates have still sold for a lot of money, e.g. AR53 NAL (for Arsenal football club), MR51 NGH for an Indian buyer, DE51 RED, YE51 CAN. I think I read that any plates starting BO08 where banned, though, so no BO08 IES.
Anyway, in the UK, plates stay with the car, not the owner, but they can be transferred as well, so there is a market for plates that spell words. You can transfer an old plate onto any car that is newer than the date the plate was first issued - so you can put an old JIM 1 plate on a new car, but not AR53 NAL on a car from 2002, for instance.
And you can’t, as in the USA, choose any combination of letters or numbers - it has to be a proper plate that fits the system. Originally you could only buy “old” plates if they had actually been issued in the year they should have been, so you couldn’t go back and buy PWN 3D if it was never issued in the 1960s, but I think they relaxed those rules in order to make more money…