The Sign (linguistics) reference article from the English Wikipedia on 24-Jul-2004
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Sign (linguistics)

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In general linguistics Ferdinand de Saussure described a sign as a combination of a concept and a sound-image. A sound image is something mental as it is possible to talk to oneself without actually moving the lips. But normally the sound-images are used to produce an utterance.

So a sign consists of

Source:
Ferdinand de Saussure, Course in General Linguistics; Part One - General principles; chapter Nature of the Linguistics Sign