Your right...it is a ring but it is a marines ring...
From Contactmusic.com ;
http://www.contactmusic.com/story/tom-s ... er_3873843
Actor Tom Selleck credits his superstitious rituals for helping him get into character for his U.S. Tvshow Blue Bloods.
After taking on the role of Frank Reagan in 2010, the Magnum, P.I. star bought a few pieces of jewellery to wear on set to help him feel more connected to his New York City Police Commissioner role.
He says, "I had a lot of them (rituals) when I started doing the character, now when I dress it helps.
"And I'm superstitious, I bought a real Marine Corps ring, because he's a marine and before the show started I thought, 'I'm going to take a risk and maybe it'll make the show work,' and I bought a watch...I popped for a used Rolex watch and I had it engraved, but I wanted it to be like a real thing."
Selleck had the watch engraved as if his Tv show children had bought it for him.
It reads, "For our pop Francis Reagan, congratulations chief, Danny, Erin and Jamie."
Kimbosan
Kimbosan