In the IMAX prologue, the Joker is seen escaping the bank heist in a yellow school bus conspicuously marked "District 22." The camera lingers on it a little too obviously, so I went a-snooping. It turns out that on http://www.gothamusd.net/, an old update on the nav bar says this: I'm thinking the Joker hijacks the reroute to suit it for his own devious uses. It probably doesn't mean anything, but I thought it was a neat detail. But who knows - the number 22 is mentioned a few more times on that site. A bit too much to be considered random.