A signature on a COMMERCIAL PAPER or document.
An indorsement on a negotiable instrument, such as a check or a promissory note, has the effect of transferring all the rights represented by the instrument to another individual. The ordinary manner in which an individual endorses a check is by placing his or her signature on the back of it, but it is valid even if the signature is placed somewhere else, such as on a separate paper, known as an allonge, which provides a space for a signature.
The term indorsement is also spelled endorsement.
Law Library - American Law and Legal InformationFree Legal Encyclopedia: Indirect evidence to Internal Revenue Code