It can be an arrangement of physical matter, including the electromagnetic spectrum, that stores the potential (when activated) to convey meaning (or a pre-specified result).
Roman Jakobson (1896–1982) elaborated the idea that the production and interpretation of texts depends on the existence of codes or conventions for communication.
This will be achieved by including metalingual contextual clues, e.g. the nature of the medium, the modality of the medium, the style, e.g. academic, literary, genre fiction, etc., and references to, or invocations of, other codes, e.g. a reader may initially interpret a set of signifiers as a literal representation, but clues may indicate a transformation into a metaphorical or allegorical interpretation diachronically.
Distinctions of class or memberships of groups will be determined by the social identity each individual constructs through the way the language is spoken (i.e. with an accent or as a dialect) or written (i.e. in sentences or in SMS format), the place of residence (see Americanisms), the nature of any employment undertaken, the style of dress, and nonverbal behaviour (e.g. through differentiating customs as to the extent of private space, whether and where people may touch or stare at each other, etc.).
Musical and iconic codes would be relevant as between a work by Arnold Schoenberg and a piece of bubblegum pop, and a painting by Rembrandt and a comic book by Frank Miller, etc.
Each medium has its own specialised codes and, by making them more explicit, semiotics is attempting to explain the practices and conventions have appeared in each form and to understand how meaning is being communicated.