Frank Reagan often states, "I'm the police commissioner. I know everything." In the Jesse Stone films, in which Tom Selleck also stars, Jesse Stone frequently states, "I'm the police chief. I know everything."
Filming nearly relocated from New York City to Toronto, because city and state tax credit programs had expired. New York State offers a program, which provides qualifying film and television productions a 30% credit for qualified production expenditures plus an additional 5% if the production is made in New York City.
The Kahr K9 9 mm pistol was an approved off-duty/backup weapon from 1998 to 2011. It was pulled from service because it could not be modified to a 12-pound NY-2 trigger pull. From 2011, Danny Reagan couldn't be carrying a Kahr K9 9mm pistol.
Most of the police cars used in Blue Bloods are replicas, bearing the obvious wrong font for the 'NYPD' lettering on the side, having blue lights and bearing the modified NYPD logo that's also worn on the replica uniforms. But in several episodes you can see the replica cars mixed with real-life NYPD police cars. Most of the time the precinct number on the real-life cars are not shown, since the NYPD doesn't allow real-life precinct numbers being used in TV shows.