The city flag of Chicago Illinois appears in the movie Ghostbuters 1984. When the Ghostbusters get thrown in jail, they discuss the strange architecture of the building where Dana Barrett lives. The other inmates listen in on their conversation and one inmate has a leather jacket with the city flag of Chicago on his right shoulder.
In the mayor's office little police marker flags can be seen all over a map of NYC. They seem to pinpoint the activity of supernatural-ghost activity.
During a montage a yellow flag can be seen in a typically NYC alleyway.