Aww… cute idea. Love how he's known (and Martin too) to wear such crazy ones, and to pass it along as a form of well-wishes. But, erm, please don't be annoyed at me saying this, but part of me kind of wondering if it would be taken intrusively, too? 
I mean, I'm sure rather than negativity in their mail, they'd find the sock thing now passed along to their kid as happy well-wishes from the fans to be a sweet thing, but it's kind of different than simply sending fan mail to the adult object of your admiration.
And yes, according to Sherlockology, that's the address (same one I used years ago), and I trust them.
