The trilogy of episodes that will make up the BBC detective drama's next run are defined by the words 'Rat', 'Wedding' and 'Bow'.
However, Moffat and Gatiss - speaking at the Edinburgh International Television Festival - would not confirm which of Conan Doyle's original stories the three words referred to.
Gatiss previously dismissed the suggestion that Sherlock would run out of suitable source material in the near future, saying: "There's an enormous amount of stuff and everything is canonical.
"The Billy Wilder film [The Private Life of Sherlock Holmes], the Basil Rathbone films - they can all be drawn upon as a Sherlock source."
Have you deduced the three Sherlock clues? Which Conan Doyle tales do you think they refer to? Speculate below!
> 'Sherlock' series three 'expected to air in autumn 2013'
Watch Mark Gatiss and Benedict Cumberbatch discuss the third series of Sherlock with Digital Spy below: