Here's what we do know...
The piece is produced on a heavy, professional-quality paper and is about 13" x 10". It's been in the same picture frame as long as anyone can remember, so the odd notation in pencil on the back (seen here) is at least 60-some years old, if not original to the art.
Here's what I've been able to guess/infer...
The hyper-stylized signature and the stippling in the banner suggest to me that it's from a professional artist, and not just someone who could draw pretty well. The style of clothing pictured points to the early 1900s, and that would be consistent with my great grandfather's life -- he was born in 1885 and his father died in 1905, so it seems as if it was a piece of art that he obtained in his 20s or 30s and held onto for the rest of his life. Given how much he moved towards the end of his life, it clearly held some importance/significance to him.
My family had, by the early 1900s, been living in the Cleveland area for several decades, and they generally remained in the area for many decades after that, which would suggest a Cleveland area artist. The signature seems to read "C. Pimmelman" but I can't find any cartoonists by that name (or any variation like "Himmelman" or "Dimmelman") working in the Cleveland area in that time period. The staff cartoonists for The Plain Dealer that I'm aware of have names that bear no similarity to the signature here.
My mother's initial guess was that this cartoon was in reference to the Teamsters union, which her great grandfather helped establish. That original union was made up primarily of draymen and delivery services people, with a strong emphasis on wagons drawn by mules and/or horses. That might be what "The Wranglers" in part refers to.
There was also a pro-union newspaper called The Cleveland Citizen that began in 1891. I can't find any references to specific artists who worked there, but I did find some text references to editorial cartoons that were run in that paper.
The two main figures are clearly intended to be caricatures of real people. I can't really guess who. Maaaaybe the Teamsters first president, Edward Murphy, but the only pictures I can find of him are from years later and he's wearing glasses. There was a pretty big fight between the Teamsters and the Building Trades Council, but that didn't occur until the mid-1930s and I don't think the clothing would be very accurate for that period.
So that's what I've got. One piece of art from between 60-120 years ago by an unknown artists about an unknown subject for an unknown purpose. Well, that and a zillion guesses, assumptions and questions. I know this is a long shot, but does anyone have any thoughts or ideas about the origins of this piece?
UPDATE: Mom found a Carl P. Himmelman that worked at the Singleton-Hunting ad agency for a few years before joining the advertising department of The Plain Dealer in 1917. Here's his 1963 obituary...