Mo. Rev. Stat. § 21.250
When a bill that has passed both houses of the general assembly is returned by the governor without his signature, and with objections thereto, and upon a reconsideration, passes both houses by the constitutional majority, it shall be authenticated as having become a law, by a certificate endorsed thereon, or attached thereto, in the following form:
This bill having been returned by the governor, with his objections thereto and, after reconsideration, having passed both houses by the constitutional majority, it has become a law, this ______ day of ______
Which, being signed by the president of the senate and speaker of the house of representatives, is sufficiently authenticated, and the bill shall be deposited with the laws in the office of the secretary of state, by the presiding officer of the house in which the bill originated. Unless the bill provides otherwise, it shall become effective thirty days after approval by constitutional majorities in both houses of the general assembly.
§ 21.250, RSMo