This will of course vary from state to state-- Each state makes its own rules.
As mentioned, Illinois uses the slash Ø for ham radio calls from zero land.
This would be CO, IA, KS, MN, MO, NE, ND & SD.
I don’t recall seeing that character on any non-amateur plates.
As a radio amateur, I occasionally consider getting the ham plates on my car.
This thread made me check the State of Illinois page on this and there’s a sentence I don’t understand (I’ve underlined it below). Does anyone know what this means?
In NZ this problem was eliminated back around 1999/2000 when the two letter four digit sequence was exhausted and the three letter three digit sequence commenced. From that time zeros had a diagonal through them. The digit 1 has never looked like an I on NZ plates.
New-style British plates use exactly the same character for 0 and O, but they don’t use the letter I (except on Northern Irish plates, I believe, but that’s another story).
Because plates follow a specific pattern of letters and numbers, though, you can tell which is which.
E.g. this is OO07 OOL.
OO is a letter code indicating Oxford. 07 is the date code indicating March - September 2007. OOL is a random set of three letters.