You know what a billiken is.
Your pizza crust is thin like a cracker and cut into squares, and covered with a gummy cheeselike substances that locals claim is "Provel".
You bleed blue.
You know how to get to the Hill, Soulard, Laclede's Landing and Ted Drewe's, and why you want to.
You hear the name "Schlafly" and you think of beer.
You've heard of bands like Head East, Shooting Star, Colony, and Dr. Zhivegas.
You know you can go to Washington University without going to Washington.
A native might have done a better job, but that's a start. Maybe some of the usual suspects can help. Or how about that St. Louis expatriate known as VodkaPundit, or globetrotting recent visitor Tim Blair?
Addendum: How could I forget the Dirt Cheap tobacco and liquor stores? Ya gotta love a place that advertises that "the more she drinks, the better you look".