Such a sign has two parts: a signifier, the form; something signified (signifié), what is referred to, the meaning.
Two kinds of relations hold between signifié and signifiant: on the one hand a reciprocal relationship, which means that the sound sequence automatically evokes the concept linked to it and vice versa.
Which signifiant is used for which signifié is solely based on an ‘agreement’, a kind of ‘contract’, as it were, between the members of a speech community.
When the analysis of images is further specified the meaning, the signifié, has to be considered more and more.