A signifier is a perceivable cue (a mark, colour, shape, sound or motion) that tells a person where an action is possible and how to perform it. Don Norman introduced the term into interaction design to separate it from the affordance, the action that is actually possible: the ledge affords climbing; the yellow paint on its edge is the signifier that says so (Norman, “Signifiers, not affordances”, interactions, 2008; and The Design of Everyday Things, revised and expanded edition, 2013). He made the distinction because designers had started saying “affordance” when they meant “cue”.
In games, signifiers are the visible layer of player-guidance: yellow or white paint on climbable edges, cracks on breakable walls, a glow on interactable objects, Mirror’s Edge’s “runner vision” turning the route red, a chime near a collectable. The course lecture series groups these as visual, auditory, spatial and learned (conventions such as red barrels exploding), and links them to Norman’s visibility principle (course lecture series, see source-player-psychology-lectures).
Two practical consequences: a false signifier (something that looks interactive but isn’t) breaks trust, so signifiers must be applied consistently; and signifiers can be too loud. The long-running debate about yellow paint is a debate about how strong a signifier should be before it feels patronising and takes away the player’s sense of finding the way themselves.
Related: affordance, player-guidance, gestalt-principles-ui, ui-design, level-design, semiotics-of-games, lighting-for-mood-and-guidance