Mo. Rev. Stat. § 400.3-205: Special endorsement — blank endorsement — anomalous endorsement.

(a) If an endorsement is made by the holder of an instrument, whether payable to an identified person or payable to bearer, and the endorsement identifies a person to whom it makes the instrument payable, it is a "special endorsement." When specially endorsed, an instrument becomes payable to the identified person and may be negotiated only by the endorsement of that person. The principles stated in Section 400.3-110 apply to special endorsements.

(b) If an endorsement is made by the holder of an instrument and it is not a special endorsement, it is a "blank" endorsement. When endorsed in blank, an instrument becomes payable to bearer and may be negotiated by transfer of possession alone until specially endorsed.

(c) The holder may convert a blank endorsement that consists only of a signature into a special endorsement by writing, above the signature of the endorser, words identifying the person to whom the instrument is made payable.

(d) "Anomalous endorsement" means an endorsement made by a person who is not the holder of the instrument. An anomalous endorsement does not affect the manner in which the endorsement may be negotiated.