Thanks for the photos anon. The second one is best for this and shows it to have the Branson family crest which makes complete sense now. A signet ring was originally a seal ring and I wonder if he actually uses it for 'special' correspondence.
I understand that because of the ease of interception of electronic communication these days many in the spy game are returning to the old tradecraft ways. Personal meetings, hand delivered messages (written/verbal), dead drops etc. It could well be a one off design specific to him alone. Perhaps even slight variations for every day of the week?
Family: Branson
Motto: "Moriens sed invictus", Dying, but unconquered
Blazon: A Cubit Arm Holding In The Hand A Scorpion
http:// www.myfamilysilver.com/Signet-Rings/