Mo. Rev. Stat. § 304.291: Rules for pedestrians controlled by special signs.

Whenever special pedestrian-control signals exhibiting the words "Walk" or "Don't Walk" 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) 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 island while the "don't walk" signal is showing.