initials (root: initial)

CIDE DICTIONARY

initials, n. pl. 

 The first letters of a person's first and last name, and sometimes also the first letters of the middle name or names; as, sign your initials in the margin; people identified only by their initials.  [PJC]

THESAURUS

initials

ID card, John Hancock, X, autograph, badge, calligram, calling card, card, christcross, cipher, countermark, countersign, countersignature, counterstamp, credentials, cross, device, dog tag, endorsement, hand, identification, identification badge, identification tag, letter of introduction, mark, mark of signature, monogram, press card, seal, serial number, sigil, sign manual, signature, signet, subscription, tessera, visa, vise, visiting card