>>240 It's most likely a prop he wore off set. Probably ran out for a quick coffee break and either forgot to take it off or decided to leave it on to mess with his fans. ;) He hasn't had it on in any other photos, so I doubt it's his... looks a little cheap, too.

His character in Crimson Peak wore a ring too (a signet ring with a crest or something), and he had it on in a couple random pictures while he was wearing his street clothes during. Apparently it's just something he does.