At the south end of the bridge across the Missouri River, Missouri 100 joins with Missouri 19 on Market Street through Hermann. The unusual mounting of these signs was done to accommodate a pedestrian and bicycle path along the west side of the bridge. The bridge was completed in October 2007, and named for longtime senator and former governor Christopher Bond.
Also note the "pointy" style marker, indicating that those markers are still part of the standard MoDOT repetoire, even though they're not as common as the what I've called the "regular" style of the Missouri outline used on state route markers. Beyond that, you can also see the different font sizes used for the numerals on the signs: the 100 is noticeably bigger than the 19.
Finally, the Missouri state outline on the Missouri 100 appears to have been "stretched" to fit the rectangular sign blank. Look at the Bootheel, which seems to be wider on the Missouri 100 marker than on the Missouri 19 marker.