For Shame!

Take one index finger, and point it at someone. Take the index finger from your other hand, and lay it across the first, at the first knuckle. Then repeatedly sweep the second index finger towards the other person. And you have to shake your head sadly and say, “Shame, shame.”

It’s a familiar gesture, but…where the hell does it come from? What does it mean, symbolically?
WAGs and whacked-out theories welcome.

This has been asked before, without conclusive answer.
http://boards.straightdope.com/sdmb/showthread.php?threadid=108580
http://boards.straightdope.com/sdmb/showthread.php?threadid=51897
http://boards.straightdope.com/sdmb/showthread.php?threadid=35497

I can’t add anything except this mention of it in the dictionary of the Center for Nonverbal Studies: http://members.aol.com/nonverbal2/point.htm