Mo. Rev. Stat. § 300.160: Pedestrian control signals.

Whenever special pedestrian control signals exhibiting the words "Walk" or "Don't Walk", or appropriate symbols, are in place, such signals shall indicate as follows:

(1) "Walk" , pedestrians facing such signal may proceed across the roadway in the direction of the signal and shall be given the right-of-way by the drivers of all vehicles;

(2) "Wait" or "Don't Walk" , no pedestrian shall start to cross the roadway in the direction of such signal, but any pedestrian who has partially completed his crossing on the walk signal shall proceed to a sidewalk or safety zone while the wait signal is showing.