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
Dedication - S1-E15
Continuity mistake: At the start, Frank isn't wearing glasses at the table. Then in one shot he is. Then not again. (00:00:40)
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.
More trivia for Blue Bloods
Question: What is the pin Mayor Dutton is wearing?
Answer: The Seal of the City of New York.