Even with two different types of state highways in Missouri, sign goofs mixing up numbered routes (with state outlines) and lettered supplemental routes (with square outlines) are rare.
I took a wrong turn off Interstate 29 near Kansas City International airport. As luck would have it, I found this marker for Route D, which is the access road to the airport. Route D also serves as a short connector between Interstate 29 and the north segment of the Interstate 435 loop.
This is the first such sign goof that I've personally seen. There have been some in construction zones. This sign, however, appears permanent. A closer look (below) shows that it even uses the "pointy" state outline that's usually found only at or near freeway interchanges.
These photos were taken on March 6, 2003. It had snowed the previous evening.