Mo. Rev. Stat. § 307.192

The operator of a bicycle shall signal as required in section 304.019, except that a signal by the hand and arm need not be given continuously if the hand is needed in the control or operation of or to control or operate the bicycle. An operator of a bicycle intending to turn the bicycle to the right shall signal as indicated in section 304.019 or by extending such operator's right arm in a horizontal position so that the same may be seen in front of and in the rear of the bicycle.