A different, simpler version of the game that springs to mind would be to restrict all allowable symbols to the ten digits, the four basic operations of arithmetic, the equals sign, and parentheses. A further simplification would be to disallow the use of any numbers greater than 9 by requiring all numbers to be broken down into their separate digits.

I don’t know, this last suggestion might be way too liberal. It gives rise to a potentially interesting and difficult (or even impossible) mathematical counting problem: For n > 1, given n randomly selected digits (not necessarily all distinct), what is the probability that they satisfy some equation of the above type?

Another potentially interesting thing to look for would be long strings of consecutive valid signs occurring on a single stretch of roadway.

Lastly, I don’t think tautologies like “7 = 7″ should be disallowed and I’d probably even allow signs with one digit, but again, I’m just guessing at this point…let me take a closer look at what’s out there, with this newfound perspective in mind!