In "The Sign of Three" (1:11:58), John says to Mary that "Vatican cameos!" is code for "Battle stations."
This is plainly incorrect. In its previous and first usage in "A Scandal in Bohemia," "Vatican cameos!" is obviously "Duck and cover!" (or whatever British equivalent of which I am unaware but that John and Sherlock would employ).
If, when Sherlock yells "Vatican cameos!" you merely assume your battle station, you're dead.