I am not sure if the hook 'em horns has anything to with the Skull and Bones society. But regarding the organization I have an interesting link that you might find intriguing.
http://www.cbsnews.com/stories/2003/...in576332.shtml
If the Skull and Bones society is present at that Texan school then I would say that maybe their use of the hand sign and saying has their origins in the Skull and Bones.