Holy f… I thought John was just smirking to himself about the corrupt nature of government. But this is just proof; Mycroft really is smarter than Sherlock. The warehouse wasn’t just a babysitting interview and salary negotiation, even if Sherlock thought it was. it was a damned test, and John passed. He’s too morally driven to sell Sherlock out, and therefore not inclined to stab Mycroft in the back. Four for you, Mycroft. You go, Mycroft.
(Also, CONTINUITY, Mr. Gatiss. You’re doing it right.)
This is an ancient Roman amulet for luck. Yes those are flying penises.
Also of note, the Roman god of marriage, Mutunus Tutunus, whose name is derived from two Latin slang words for penis. His name is essentially Dick Wiener. If you have ever wondered just how much like us the Romans were, read the etymology section.