Michigan State Highways are designated as M and a number. Michigan and Kansas are the only two states that use the state letter to designated highways. The signs are a black and white diamond with a Block M at the top. They used to be just diamonds but at some point that changed.
M-22 was established in 1919 and is one of the original state highways. It goes from Manistee to Traverse City by circling around the Leelanau Peninsula. It follows along the shoreline and passes through the Sleeping Bear Dunes. There is also a clothing company by the same name. Sometimes you will see cars with M-22 bumper stickers.