Character mistake: Officer Rachel Witten tells Eddie the gun she has belonged to her dad when he was on The Job. In episode 15 of season 8 Gormley tells Frank that Witten's dad was a FDNY Battalion Chief and her uncles were police officers. In episode 12 of season 9 Officer Witten's dad Sgt. Scott Witten speaks to Frank about being on The Job. It's unlikely and not normal for someone to become a firefighter after being a police officer or vice versa or do both jobs.
Continuity mistake: Danny and Linda are hugging after Danny tells the boys to go pay your respects to the WWII Memorial. In the next shot they are standing apart as when he told them to go pay their respects to the memorial. (00:54:34)
Other mistake: Throughout the episode, all the interactions with the characters went from day to night except for Commissioner Reagan chaperoning his grandson's class at the museum. It stayed daylight the whole time at the museum. (00:27:14)
Other mistake: Jamie races to the patrol car after witnessing a car jacking with possible child inside. He flings the door open, gets halfway inside, and the car starts without him even being close to turning the key in the ignition. (00:04:00)
Answer: The Seal of the City of New York.