 FAIR: 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 dont 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.