It has now been confirmed by BBC1, the third series finale of "Sherlock" will be titled "His Last Vow".
The title sounds like a reference to Arthur Conan Doyle's short story "His Last Bow" which is more of a spy story than the usual murder mystery elements of Doyle's other stories.
Some tweaking will have to be done though - the story is chronologically the detective's final case in the series.
Steven Moffat penned the episode which Nick Hurran ("Doctor Who") will direct. Filming on the episode commences in two weeks.
The first two episodes - "The Empty Hearse" (based on "The Empty House") and "The Sign of Three" (based on "The Sign of Four)" have already been shot.
Source: Digital Spy