Well I figured out the beginning with the symbols because I like languages, but other than that not really My theory is long and would take forever to type so I'll just copy and paste from someone whom I agree with.
We see Sherlock on his mobile at the top of the building, this is definitely Holmes. When Sherlock first looks over the edge and asks “for a moment by myself”, there’s a bus parked alongside the hospital. After a minute or so, and next time we look down, there’s a lorry full of bin bags there. He was obviously stalling until the lorry full of rubbish bags is in position.
Watson is below on the street talking to him and is told not to move and to keep his eyes on Holmes so he doesn’t see the upcoming body switch. Holmes jumps from the building and seems to land on the pavement below. Actually he has jumped and landed in the back of the lorry full of rubbish bags and another body is put in his place on the pavement, which, conveniently is hidden from Watson’s view behind the rubbish lorry. Look at when he jumps. WAY too far from the building considering where the body ends up on the pavement (also, jumping forwards, despite the body being side on), and as we pan to the body, the lorry full of rubbish bags (to pad his fall) is driving away, with Holmes in it. The "Holmes" which we see landing on the pavement is in fact a dead body dressed up to look like Holmes, which he collected from Molly at the morgue. Watson then runs to Holmes but is disorientated by a "random" cyclist. Also, don’t forget that Watson sees what he expects to see, considering he’s just witnessed Sherlock jumping off the building, ie Sherlock’s dead body, it wouldn’t occur to him that it could be anyone else.
So, who is on the ground then? Well, his double. His double being the guy that Moriarty used to kidnap the children, hence the children being scared of him despite having never met Sherlock before. I’m assuming a double as opposed to a mask at this point, as I expect a mask to be too loose of a plot line. That said, in the last episode, “The Hounds of Baskerville”, whilst in the Baskerville facility, “human cloning” was mentioned. Could be a bit tenuous, but you never know.
He went to Molly just before the end so that he could ask her a favour so that she could perform the autopsy and “verify” his death, even though it didn’t occur. << I saw this somewhere on l'internet while I was thinking over my theories- couldn't agree more. I still hope it's more clever than that though... I would hate to have figured it out already