Mo. Rev. Stat. § 300.220: Authority to place and obedience to turning markers.

1. The city traffic engineer is authorized to place markers, buttons, or signs within or adjacent to intersections indicating the course to be traveled by vehicles turning at such intersections, and such course to be traveled as so indicated may conform to or be other than as prescribed by law or ordinance.

2. When authorized markers, buttons, or other indications are placed within an intersection indicating the course to be traveled by vehicles turning thereat, no driver of a vehicle shall disobey the directions of such indications.