Over the course of the series, it is repeatedly established that Danny is the oldest of the four Reagan siblings followed in order by Erin, the deceased Joe, and then Jamie. There are a few certain episodes, however, where Frank mentions in conversation that Joe was the oldest.
Jamie and Eddie are regularly seen in a Ford Crown Victoria Police Interceptor while en-route to a call, however, when they arrive at the scene, they are in a Chevrolet Impala.
Jamie had a gold ribbon/medal bar on his uniform. When he made Sargent that bar went missing. It is never addressed at all.
Several police cars have forward facing blue lights. NYPD does not use forward facing blue lights on any emergency vehicle, and state law prohibits blue lights facing forward on police vehicles.
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.
The NYPD Major Case Squad does not operate at the precinct level. Its detectives are stationed at One Police Plaza.
For the NYPD, the Police Commissioner has the rank insignia of Five Gold stars.
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.