Visible crew/equipment: As Danny gets out of the car, with the bad guy who shot Erin in the courtroom, holding her hostage and coming out to meet him behind the courthouse, as Danny gets out of the car, in the driver's side car door mirror you can see a crew member in a red shirt holding one of those "scene marker" slap boards. (00:32:40)

Blue Bloods (2010)
1 visible crew/equipment mistake in season 4 - chronological order
Starring: Tom Selleck, Bridget Moynahan, Donnie Wahlberg, Len Cariou, Will Estes

The Uniform - S2-E11
Character mistake: While handcuffing an auxiliary officer in his apartment, there is a poster on the wall reading, "attention military personal..." Personal is misused. It should read "attention military personnel." (00:16:02)
Frank Reagan: And I don't have a Teflon suit. Everything gets to me. Every time one of ours is hurt, or jammed up, or he's in over his head, it gets to me. I just don't show it, 'cause I can't show it, 'cause nobody wants, or needs, a sensitive police commissioner.
Sid Gormley: OK.
Frank Reagan: So screw you!
Sid Gormley: Yes, sir. That an order, too?
Frank Reagan: Yeah, that's an order.
Sid Gormley: Screw me. I'm on it, boss.
Trivia: Although Len Cariou plays Tom Selleck's father, he's only five years older than Selleck.
Question: What is the significance of the lapel pin worn by detectives on Blue Bloods?
Answer: It is an NYPD Detective Bureau lapel pin. If you zoom in on a pic of "Danny Reagan," you will see that the pin has the letters DB on it.





Answer: It is the lapel pin worn by members of the NYPD Honor Legion.
The lapel pin is on Danny but not Biaz, why? Also, Baker, Sid, Frank &Garrett wear one. Significance? Are they all the same?
Is the P.C.'s pin different than a legion pin? What are the symbols and their meaning?
I think it may be Masonic?
But why would the mayor wear one?