Nabokov Smiles?

In a discussion about the origin of the (in)famous 'smiley face' [ i.e., ":)" ], I found the following. It appears to be a Nabokov quote, although it is uncorroborated [ ed: now it has been ]:

Q: How do you rank yourself among writers (living) and of the immediate past? Nabokov: I often think there should exist a special typographical sign for a smile – some sort of concave mark, a supine round bracket, which I would now like to trace in reply to your question.