Martin Freeman admitted in the London Apple store interview that he was really surprised to see the scene in the final cut because he only did the whistling (and pointing?) to make Benedict Cumberbatch laugh.
And that’s why I’ve got this nebulous feeling that they acutally erased a line. The original script might have looked something like this:
TESSA: Which one of you is Sherlock Holmes?
SHERLOCK: Dr. Watson is the handsome one… so I’m Sherlock Homes.
This would have been a perfect reference to a line in The Private Life of Sherlock Holmes:
GABRIELLE: Which of you is Mr. Holmes and which is Dr. Watson?
HOLMES: Dr. Watson is the handsome one.
Rethink this. In the Rizla game Sherlock is unable to deduce that he has written his own name at his forehead. And when Tessa asks “Which one of you is Sherlock Holmes?” Sherlock concludes “John (Dr. Watson) is the handsome one” (or “John is the pretty lady”…) “so I must be Sherlock Holmes”. He would have answered Tessas (and John’s!) question and finished the game at the same time.
That this is only a head canon makes me kind of sad.