“When have we passed over into the order of the signifier? The signifier may extend over many of the elements within the domain of the sign. But the signifier is a sign that doesn’t refer to any object, not even to one in the form of a trace, even though the trace nevertheless heralds the signifier’s essential feature. It, too, is the sign of an absence. But insofar as it forms part of language, the signifier is a sign which refers to another sign, which is as such structured to signify the absence of another sign”.
The master-signifier, which acts as that around which our reality is structured as the symbolic order or “big Other”, lacks even its opposite, which therefore becomes the impossible objet a of drive.
This rather tortuous notion can be dismantled quite easily via Lacan’s discussion of the “Rat Man” and the obsession over his replacement pince-nez. The obsession surrounds the repayment of a debt. The “barred S” of the master-signifier and its inverse, the objet a, represent that which structures reality (world) and the object of drive, both of which are radically absent or at least unattainable, hence the “barred” nature of each. The term we usually use for what structures reality as a whole as world is “god”, while as self-insistence, the object of drive or “objet a”, can only be the self itself.
Thus the “barred S” of the master-signifier is the representation of the identity of the god which structures reality, around which the obsessions of the “Rat Man” circulate as misdirected drive. The barred S as signifier, as the god that structures the symbolic order which in turn is constitutive of reality, is a simple and well known symbol – $.
As a signifier, it is a sign that points to an absence that is not a trace or an absence of something once there but there no longer, but an absence of something never there; something not even properly nameable. It is the signifier of pure difference, which founds self-identity in the minimal difference between recurrences of the self-same.