Photo courtesy of David Herman (taken July 2006)
There's plenty of room for the route numbers on this set of markers where Missouri 21 intersects with US 50, US 61, and US 67 (Lindbergh Boulevard) in St. Louis County. Also note that the Missouri 21 is in the "pointy" style more often used for route markers on freeways.
This sign assembly also shows off one of Missouri's few triple concurrences involving US routes. The southeastern most six miles (or so) of Lindbergh Boulevard are designated US 50, US 61, and US 67.