Ferdinand de Saussure defines the lingual sign as made up of two parts that form the whole sign (here you can read about de Saussure's definition of the sign). Saussure actually saw the division of the sign into sound image and concept as a bit ambiguous. So he refined the idea by saying it might make things clearer if we referred to the concept as the signified and the sound image as the signifier.
Saussure shifted the emphasis from the notion that there is some kind of 'real world' out there to which we all refer in words and is the same to all of us. Obviously, a language community has much of this real world in common, otherwise we couldn't communicate. But while de Saussure is definitly not one of those philosophers who deny material reality, he does say that when it comes to the nature of the lingual sing relaity in itself does not play a part. Lingual sings according to de Saussure do not reflect reality, and language does not simply describe the world. Language for de Saussure is a system of interalitions between signs and between signifiers and signifieds. This is very important in the broader context of de Sassure's theory and Structuralism. The signifier does not point to an actual entity in the world, it points only to the mental meaning called signified.
For more on the nature of the sign an de Saussure's thought: