Mo. Rev. Stat. § 307.140: Safety glass on vehicles for hire and school buses.

It shall be unlawful after January 1, 1936, to operate on any public highway or street, in this state, a motor vehicle registered in the state of Missouri, manufactured or assembled after said date, designed or used for the purpose of carrying passengers for hire, or designed or used for the purpose of carrying school children, unless such vehicle be equipped in all doors, windows and windshields with safety glass.