1The act of placing a signature on the back of a negotiable instrument in order to assign it to an indorsee. 2 The signature itself. accommodation indorsement. A signature by a third party who is neither the payor or the payee, but is acting to guarantee payment by the former. blank indorsement. A signature that names no payee, thereby making the instrument payable to the bearer. restrictive indorsement. An indorsement placing special conditions upon the assignment of the instrument. special ...