Here's a nifty wrapper that helps explain what the mysteriously-named Zero Bar is all about. Something about a cool, tasty treat... y'know, so cool it's like zero degrees. This wrapper's copyright is 1931, a quaint time in which children dreamed of saving up for The Whizzer, "a real steam engine that runs!" Nowadays, most kids probably don't know what a steam engine is or what it would be good for.
And here's a closer look at the steam whistle offer: