Sherlock producers today revealed that the title to the second episode of the third series will be The Sign of Three.

http://www.radiotimes.com/news/2013-04-10/sherlock-series-3-episode-2-title-revealed-as-the-sign-of-three

Looking back at the original “rat, wedding, bow” clues, it certainly does seem to point towards the fact that the “wedding” will be John’s wedding to Mary, particularly given this new choice of title.

However, with Moffat, nothing is certain and I won’t believe anything until I see it on screen!