Digging through articles and photos from the 1920s, I later found two images of the jug displaying a pointed Minnesota "M": one in the program for the 1923 game, and another 1927 photo of Minnesota captain Herb Joesting cradling the crock. Since both images predate the shady doings of the early 1930s, I'm confident the jug in Michigan's custody is authentic.
I'm also certain that for at least two years in the 1930s, the U-M tried to pass off a replica as the real thing. I don't know who created the "Cadillac" jug, or where the real trophy was at the time. For what it's worth, though, Minnesota's Oscar Munson never had any doubt: he always claimed the Little Brown Jug had spent those years "in Mr. Yost's cellar."
[Originally published in November, 2009.]