A
sign is an
object,
quality, event, or
entity whose presence or occurrence indicates the probable presence or occurrence of something else. A natural sign bears a causal relation to its object—for instance,
thunder is a sign of storm, or medical
symptoms signify a disease. A conventional sign signifies by agreement, as a
full stop signifies the end of a sentence; similarly the words and expressions of a
language, as well as bodily
gestures, can be regarded as signs, expressing particular
meanings. The physical objects most commonly referred to as signs (notices,
road signs, etc., collectively known as
signage) generally inform or instruct using
written text,
symbols,
pictures or a combination of these.