Michigan Highway 137 was a tiny spur southward, from an east-west section of US Route 31, into Interlochen. This is just southwest of Traverse City. Technically, Michigan Highway 137 doesn't exist anymore, as it was decommissioned in 2019. But I took photos for my route collection in 2018, so I'm keeping it in there! Michigan Highway 137 was seriously short, at a length of about two miles. The southern end was the entrance to Interlochen State Park, and the northern end was at US Route 31. Though Michigan Highway 37 lies only about four miles to the east, I don't think Michigan Highway 137 was named after Michigan Highway 37.
My photo of Michigan Highway 137 shows the first southbound reassurance marker at the northern end of the route. Again, because Michigan Highway 137 is now decommissioned, this sign assembly likely no longer exists. But travelers would have used this sign to recognize that they have successfully turned onto Michigan Highway 137 from US Route 31. This photo was taken in March 2018 during a trip to the Traverse City area.