Green’s Dictionary of Slang

(US black) one who boasts or makes insulting remarks.

1933		C. Himes ‘Prison Mass’ in Coll. Stories (1990) 150: He had earned the name of ‘Signifier’ by his habitual scoffing and jeering of all things sundry which passed before his attention.
1956		H. Gold Man Who Was Not With It (1965) 87: No F.O.B.’s, C.O.D.’s, junkies, lushes, agitators, and collect telegrams. I’m the only signifier I need around here.
1964		R. Abrahams Deep Down In The Jungle 54: The monkey is a ‘signifier,’ and one of the methods he uses for inflaming the lion is to indicate that the elephant has been ‘sounding’ on the lion.