A 24-sheet is essentially a billboard. I have never seen one, but this is the image from the campaign book. Size of a 24-sheet is 108"x246" - that's 9 feet tall and 20.5 feet long!!
What I do have is this page from some unknown magazine that illustrates the Alice 24-sheet. The ad is for what appears to be a trade association for outdoor advertising companies called The Standard Group of Outdoor Advertising Companies.
I hesitated to post this ad, mostly because of the headline, which sounds like bad ad copy for a 1970s porno.
If this is really what the billboard looks like, would be great to have one...Alice would be something like 8 feet tall!