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)
Nightmares - S3-E7
Visible crew/equipment: While Jaime talks to Malcolm on the street and takes his picture it's being filmed from two camera angles. When Malcolm shoves Jaime and he falls to the ground we can see the second camera's tripod leg at the right side of the screen, and as Jaime gets up we can see the second camera as well.
Visible crew/equipment: After Baez tells Danny that detectives from Moscow are on their way to help with the investigation, when it cuts to Anthony entering the courtroom, just as Erin removes her glasses the T-mark is visible on the floor behind her, at the bottom left side of the screen. (00:08:35)
Visible crew/equipment: After the opening credits, when it cuts to Frank's office a red tape mark is visible on the floor near the window, at the right side of the screen. After Nicky leaves the office it appears Frank walks to that area to look out of the window. (00:04:35)

Visible crew/equipment: When Eddie and Jamie stop to help the woman holding the boy, in the exterior shot as Jamie gets into the back of the RMP with the young boy, the reflection of camera equipment is visible on the window. (00:04:55)

Visible crew/equipment: After Anthony drives the Porsche 911 into the garage, in the shot facing Erin and Anthony just as Jimmy gets into the car, the green T-mark, the red tape mark, and blue tape mark are visible on the floor.

Visible crew/equipment: When Danny and Baez are at the scene of the firebombing while it's raining, in the second shot as they walk toward the eleven body bags, three nylon T-markers (yellow, red, and green) are visible on the wet ground where Baez, Danny, and Molina will be standing in the following shots. (00:02:45)
Visible crew/equipment: After Danny tells Linda all that matters is her brother is alive and her family is safe, when it cuts to the courtroom there's an overhead shot from behind Frank, and the actor's yellow tape mark is visible on the floor at the left side of the screen. (00:34:20)
In and Out - S7-E14
Visible crew/equipment: While Danny and Baez are hiding in the hall, when Ramirez (parole officer) knocks on Lloyd 's door he gets the gun from under the seat cushion, then as Lloyd starts to walk to the door, the green T-mark is visible on the floor near the right side of the screen. (00:34:20)
The One That Got Away - S7-E13
Visible crew/equipment: After Eddie tells Jamie that she wanted Josh to swoon over her like Caroline seems to be doing with Jamie, when it cuts to Erin as she tells Danny that Child Services will likely release the boy to his parents, as Danny says, "Hold on," the green T-mark is visible on the floor. (00:22:30)
Confessions - S7-E9
Visible crew/equipment: While Frank visits with the Cardinal to tell him about the time sensitive situation, when Frank asks about St. Mary's surveillance cameras as they both sit down, the small green T-mark is visible on the rug under the Cardinal's chair. (00:23:40)
Visible crew/equipment: After the family dinner, when it cuts to Jamie standing at the sink loading the dishwasher, the green T-mark is visible on the floor behind his feet. (00:29:10)
Visible crew/equipment: At the start, when Erin is interviewing Miranda they take a break, and just as Miranda says she's starving and stands up, the red T-mark is visible on the floor in front of Anthony's feet. (00:00:55)
Visible crew/equipment: When Danny tells the M.E. what the victim shouted prior to being hit by the car and what the word means, the reflection of the moving camera is visible on the glass. (00:07:25)
Visible crew/equipment: When Erin walks into her office and finds Robert waiting for her, as she walks past him toward her desk, the green tape mark is visible on the floor near Robert's feet. (00:01:00)
Visible crew/equipment: When Danny gets off the phone he tells Baez that a Port Authority cop has detained their guy, and at the start of the next shot facing Baez, the reflections of the moving boom pole/mic and the boom operator are visible on the glass, at the right side of the screen. (00:02:20)
Nightmares - S3-E7
Visible crew/equipment: After Jaime goes after Malcolm, who was released again from the hospital, it cuts to Danny and Kate parked in the car across the street from the church, and when Kate opens her door the reflections of the camera and crew members are visible on the window.
Visible crew/equipment: At the hospital, after Maria tells Danny about the busboy who was arrested for the same venue and same MO, it then cuts to Jaime undercover in the store. While Jaime walks toward Marco, the dealer at the counter, the camera moves at the same pace as Jaime, and we can see the reflection of the camera on the glass (between Jaime and the camera). (00:28:20)

Visible crew/equipment: At the safe house, while Danny and Waylon are alone with Rodriguez they "convince" him to call off his men, and in the last shot of this scene as they head out the door, the reflection of a crew member (presumably the camera operator) becomes visible on the picture hanging beside the door. (00:39:20)
Visible crew/equipment: After Danny and Baez get the hospital physician's rundown on Joe's condition, when the partners reintroduce themselves to Joe the reflection of the boom pole/mic is visible on the glass behind Danny.
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?