This is he common shorthand for the University of Michigan. Used by students and faculty alike. It is pronounced the same as the verbal abbreviation, "U of M", but takes 3 fewer keystrokes. UM is sometimes also seen, but is less common, since it can be confused with an emphatic expression of uncertainty. Perhaps U/M would make more sense, because x/y is sometimes read "x of y", but it is what it is.
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