Mo. Rev. Stat. § 290.265

A clearly legible statement of all wage rates required to be paid to all workers employed in order to execute the contract and employed on the construction of the public works shall be kept posted in a prominent and easily accessible place at the site thereof by each contractor and subcontractor engaged in the public works projects under sections 290.210 to 290.340 and such notice shall remain posted during the full time that any such worker shall be employed on the public works.