A letter of reply Steve Martin sent to a fan in the early 80's, written on his production company's letterhead. Click to enlarge.
Ha! It's hard to go wrong with self-deprecating humor when you are the higher status person in an interaction and both parties know it. Here's the source, and I thank J.Y. for the pointer.
That’s great! See also his business card: http://wehrintheworld.blogspot.com/2009/07/i-am-totally-stealing-this.html
The form used by Robert Heinlein was amusing too.
http://kk.org/ct2/heinlein.php