This apparently happened yesterday, but I just realized today that the folks of Rory's First Kiss, (aka The Dark Knight) have once again set up shop in the old Chicago Post Office by where I work.
Not only has the "Gotham National Bank" lettering gone up to replace the chiseled "United States Post Office" on the front of the building, there is also a sign on the opposite side of the building reading "Gotham Police". Apparently they are using the post office's exterior for more than one set.
The windows to the large lobby of the US Post Office has been blacked out by large "flags" (essentially large swaths of black fabric on a frame). This was the same lobby that contained a yellow school bus during the previous filming that occurred there.
Here's some linkage from Superherohype:
Crew coming back to the Post Office
On set pics, including the back of the Post Office, with the Gotham Police sign