I don't remember this one, but Mel does, and says, "It creeped the hell out of me as a kid. The little perusing I have done as to the origins revealed that it was developed to replace a skull-and-crossbones as a deterrent for drinking poisons — apparently there were some kids who thought the symbol meant that it was a drink for pirates, and, well, pirates are cool! There’s more info on Wikipedia here.
Be sure and check Mel's Video Concert Hall blog for lots of the grooviest vintage music vids you'll ever see... some of which I intend to filch for LOTD (that's filch, not felch). Mel and Lefty also run Our Tube, another site with excellent vintage vids: commercials, music vids, show opens, etc. Good stuff all around.