I haven’t really seen anyone talking about this, but it’s one of the things that jumped out at me. When Moriarty comes to Baker Street for their conversation, Sherlock prevents him from sitting in John’s chair. He is protecting John (symbolically at least) from Moriarty. Moriarty has already tried to hurt and take John from Sherlock, and Sherlock won’t allow something associated with John to be touched by Moriarty. I think it shows just how much Sherlock cares for John, and would do anything to protect him.
I noticed he didn’t let him sit in that chair though at the time I didn’t realize whose chair it was.
That is so, so incredibly sweet and subtle and beautiful.
Err. No. Sherlock points at the chair and wants Moriarty to sit in it. Moriarty refuses and takes Sherlock’s chair.