The term as it applies to literary criticism is something that scholars have had a great deal of difficulty defining, although arguable Gates does a better job than most in this piece. Essentially, as used in this text, "signifying" is linguistic trickery. The term gained prominence among African American literary scholars during and after the Black Arts Movement because of its connections to the call and response nature of the Black vernacular, but it has also been used by critics to exemplify the relationship between the signifier (the word that we use to give something meaning) and the signified (that which has meaning given to it by the word.
To help you put it ion context, here is a pretty good definition of the concept:
"Signifier" and "signified" are terms used in one branch of linguistics and literary criticism to describe the components of a sign: the signifier, to put it simply, is the word, and the signified is the thing or idea it represents. Signifiers needn't be confined to words; they can include any system of representation, including drawings, traffic lights, body language, and so on. Much of the literary criticism of the last twenty-five years has focused on the relationship between the signifier and signified, and therefore on the very nature of meaning" (Lynch, nd).
I have also included a link fot you to review that provides an excellent critical analysis of the piece. Take a look at that as well!