The Golden City Dry Cleaner sign has a phone number at the very bottom. In some shots the number '7' will be present; in other shots it will be absent.
The Chicago Police Uniforms in the show are perfect except for the Left Shoulder Patches, which 'should' read Chicago Police, but instead are a fictional patch that reads 'Police Department of the City of Chicago'. This is common when any show films in Chicago (even when most of the filming is done in Canada). Chicago has a rule that no representation of their real Police Patch can be shown without express permission from the city. Since most movie productions don't want to hassle having a bureaucrat 'approving' all of their scripts, most depictions of the "Chicago Police Department" have bogus patches versus the real thing. Thus this is an intentional "mistake" but one that sharp eyed viewers will pick up.