Answer: sign

AnswerCrossword Clue
SIGNEndorse, in a way
SIGNFinalize a contract
SIGNCommunicate digitally
SIGNDriving instructor?
SIGNTalk with one's hands
SIGNLamppost attachment
SIGNPut one's name on
SIGNSandwich board, e.g.
SIGNSpeak to the deaf
SIGNAgree formally
SIGNCommunicate manually
SIGNTalk digitally
SIGNLeo, for one
SIGNPut one's John Hancock on
SIGN"Talk" to the deaf
SIGNMake an X, maybe
SIGNA coach might flash one
SIGNLegalize, in a way
SIGNSymptom
SIGN"What's your ..?"
signgesture
SIGNA protester might carry one
SIGNIndication
SIGNOmen
SIGNInk
SIGNSpeak with the hands
SIGNWord after high or road
SIGNAgree to a deal
SIGNThis word follows the last word of 18A, 23A, 50A, and 56A
SIGN"What's your ...?"
SIGNSay "I love you" by extending the thumb, index finger, and pinky, e.g.
SIGN+ or -
SIGNTraffic indicator
SIGNTalk silently
SIGNUse Ameslan
SIGNProtester's placard
SIGNSpeak manually
SIGNAquarius, e.g.
SIGNAutograph
SIGNBillboard