A word I recently learned is "affordance". In my own words, an affordance is a visual or other cue that suggests an available action.
For example, the friction-improving bumps on a camera's battery door are an affordance that indicates that you pull to open the battery door.
Or the three diagonal lines in the lower-right corner of a window are an affordance that the window can be resized. They invite you to drag the corner with the mouse.
Wiktionary has:
affordance: an action that an individual can potentially perform in his or her environment
Coined by J. J. Gibson, apparently.