I've never heard the term "tailor's S" before, but I assume you
want to make a mitered corner. Here's a way of mitering a separate
binding that will go on a piece of fabric:
http://www.frommarti.com/miter.html
and a method that involves just the piece of fabric itself (used for
hemming curtains):
http://www.denverfabrics.com/pages/s...nd-curtain.htm

Kay Lancaster