NYPD parking on sidewalks is more of a "who watches the watchmen" problem unfortunately.
Not to mention completely opaque tinted windshields and windows, and intentionally defaced or corroded license plates..
Corruption is part of the job description, for the NYPD.
It doesn't have to be! Parking enforcement wasn't always within the NYPD's remit. Until 1996, NYCDOT was responsible for parking enforcement.