Izzy Hands + the ring around his tie
OUR FLAG MEANS DEATH Season 1
“Foad has no plans to share the backstory since he's not sure if the writing for the show might contradict it later. O'Neill similarly has a backstory to the ring that he wears around his tie that he will not share, though he does share that the choice of the stone was centered around his loss of his mother around the time of the costuming.” (source)