Mo. Rev. Stat. § 78.580

Three members of the council shall constitute a quorum to do business; but no action thereof shall be valid unless at least three shall vote in favor of such action. Upon every vote the yeas and nays shall be called and recorded and every motion, resolution, and ordinance shall be reduced to writing before the vote is taken thereon. Every resolution or ordinance passed by the council must be signed by the mayor or in his absence by the chairman pro tem, or by two members of the council before the same shall be enforced.