The original sign from the 1920s to about 1931 was an orange oval. The rendering is a hack job taken from a high-resolution scan of a 1926 MoDOT map. The shade of orange is an approximation based on the current MUTCD standard.

The next design appeared through the 1970s (source: James Lin's marker site). Later this design used the FHWA B and C fonts. During the construction of the Interstate system a version of this appeared on guide signs with white outline and text on the green background.

The next design appeared at Interstate exits through the 1970s as in this example from I-35 exit 48 south of Cameron. Picture original source: Joe Koehler, found at Mark O'Neil's Missouri page.

The current design, which has several versions today, appeared at the highway junctions in the 1960s and eventually replaced the previous markers by the mid-1980s. Some of the signs have a white border around the edge; some do not. The shield and text varied in size over time, as the photo page shows.

This is a wider version of the current design, which started appearing in 2000. Sometimes it will have B font; sometimes C.

A newer design started appearing recently that uses the shape similar to those used on freeway guide signs. It has a different routing of the Mississippi River and shows the Missouri river portion as a straight line. Notice that the southwest corner is rounded. Fellow road enthusiast Mark Roberts calls it "pointy" and has a comparison here on MO 1 in Kansas City. I just call it ugly.

Another newer design started appearing recently that uses a more detailed state outline. Usually this type appears in construction zones. The sample is on MO 58 in Raymore, MO on a stretch handled by local maintanance rather than MoDOT.

This is a sample of the method used on freeway guide signs (a "pointy" version is also used).

Missouri's secondary system was started in 1931, and the signs appeared like this sample. Early versions used block text fonts; this sample was around in the 1960s and 1970s. When the modern versions started appearing at highway junctions, these remained at county lines until the 1990s.

This "cutout" version started appearing at the Interstate exits through the 1970s. At the start of the Interstate construction, this also appeared on guide signs as white border and text on green background.

This is the design now in use. Most two-letter routes use this square sign and Series C text; newer signs use the rectangular (30 x 24) blank and series D.

This is the design now in use on freeway guide signs, also with rectangular version for two-letter routes.