Missouri Revised Statutes Title XIX. Motor Vehicles, Watercraft and Aviation § 300.240. Authority to sign one-way streets and alleys

Whenever any ordinance of the city designates any one-way street or alley the city traffic engineer shall place and maintain signs giving notice thereof, and no such regulation shall be effective unless such signs are in place. Signs indicating the direction of lawful traffic movement shall be placed at every intersection where movement of traffic in the opposite direction is prohibited.