Thirty years ago Roland Barthes and others first perceived the power of unassertive objects as "signs, " bearers of accepted opinion and of ideological manipulation. In the three decades since, there has developed a new science of signs, called semiotics. Its practitioners include advertisers, politicians, media pundits, and cultural mandarins, all of whom send signals - a product, an image, a service, and idea - to those who will "buy" only if they recognize themselves in the message.