I first encountered the concept of semiotic ghosts in William Gibson's short story The Gernsback Continuum. I don't think the concept is particular to the usual science fiction fare Gibson favours. A semiotic ghost is one way to interpret popular delusions in reference to a particular culture. It is an idea that may help in explaining many cultural phenoma and is not a specific literary concept. I think that it can also be a useful concept in general, and my hope is that this writeup will allow this specific idea to propagate.
In Gibson's short story, we are presented with a photographer who is commissioned to take pictures as evidence of the future America that never was. Shark-finned flying cars, stylised bright-coloured plastic clothing, Flash Gordon architecture, that sort of thing. The title, The Gernsback Continuum, refers to Hugo Gernsback, the "father of science fiction", and publisher of the pulp science fiction magazine Amazing Stories, famous for wild extrapolations on the course American technology of the 1930s would follow. Our hero, with a little chemical aid, begins to experience hallucinations of the fantastic futures conjured by the imaginations of science fiction writers and illustrators of decades past. His present becomes the imagined future of the past. When discussing his problem with an associate, the associate identifies these hallucinations as instances of semiotic ghosts and recommends for a cure to watch television a-plenty.
Let me explain more the meaning of semiotic ghosts. I will begin with the "semiotic" part. Semiotics, says modern Webby, is "The theory and study of signs and symbols [...]". Signs and symbols occur as part of a broader culture that tacitly agrees to identify the meaning behind them. Emphasis on culture, with different symbols and signs for different cultures. Now for the "ghost" portion. A ghost is a supernatural creature, whether one believes in them or not, an entity outside of the realm of our ordinary experience. Expanding this definition, "ghosts" could be witches, kapas, trolls, tzitzimimes, changelings, or centaurs. Some of the ghosts preferred by modern mass (Western) culture include extraterrestrial beings, vampires, sentient machines, and invincible action heros.
Putting it all together, a semiotic ghost, also known as a semiotic phantom, is an image, sensation, or hallucination that an individual may experience in accordance with the signs and symbols of the particular culture said individual shares, but that is not really there. We hear about semiotic ghosts all the time, everywhere. Some modern examples you may recognise are alien abductions, internet hoaxes, invincible computer viruses, or all-powerful teenage hackers. In other times and other places, we could have had instead visiting succubi/incubi, snake-oil vendors, fortune-tellers, and necromancers. These are very similar experiences, except that they happen to be enclosed within the semiotics of different cultures.
Semiotic ghosts needn't be as extravagant as the hallucinations experienced by Gibson's photographer. Ordinary people, noders much like you and me, can also see semiotic ghosts. Take the following example permeated by Everything2 culture: there is a dream log by kthejoker that describes a very peculiar experience that is completely encased within the boundaries of our current E2 servers (they are, by the by, aptly named spectre and willowisp). Or recall the events in the United States shortly after the World Trade Centre attacks of September 11, 2001: almost any man wearing a turban or with the wrong shade of skin tone was seen as a potential terrorist. In fact, any realisation of the mass unconscious, any piece of cultural imagery that has broken off the mainstream and acquired life of its own can be a semiotic ghost.
Ponder now, gentle reader, what are the semiotic phantoms that haunt you?