The unknown signified
Rarely, very rarely, we may encounter a signifier for which there is no clear signified. Or, none that we recognize. Usually, this occurs when someone has produced an image that is so heavily abstracted photographically that we are unable to recognize the 'original' referent system. Here is an example taken from a Helmut Lang ad. Seeing an image prompts us to realize that normally signifiers and signifieds are linked. Now to be sure there is an obscure signifed here, namely that this artsy, upscale advertiser is so avant-garde that they have no need for a conventional signified.