Spur Route 45 connecting Missouri 45 and the tiny Platte County town of Waldron isn't marked at all. But at the end of the route, just across from the Waldron post office, MoDOT has put up the standard marker indicating that, from this point forward, the route isn't maintained by the state.
There's also a marker on the other side of the (very narrow) road marking the start of maintenance in the other direction.
This photo was taken looking southbound from the end of unmarked Spur 45 in September 2008.