@Rudiger said:

Above the bookcase in Erin's office(s) is a folded US flag is it ever revealed who's service this flag represents? Given the male Reagan's in the show, I can only guess this is from her maternal grandfather & passed on from her deceased mother

I think it was Joe's, her brother that died. He was a veteran & a police officer.

@bratface said:

@Rudiger said:

Above the bookcase in Erin's office(s) is a folded US flag is it ever revealed who's service this flag represents? Given the male Reagan's in the show, I can only guess this is from her maternal grandfather & passed on from her deceased mother

I think it was Joe's, her brother that died. He was a veteran & a police officer.

I considered that initially however I don't think their's any canon that Joe served in the military, only Danny followed that tradition, so I'd consider the NYPD flag in Frank's office as commemorating Joe

Then maybe it's the one that covered his coffin? Some police departments follow the same traditions as the military. I don't know about the NYPD but they probably do?