In nonverbal indication, an observed or otherwise perceptible sign takes the place of a spoken word. Different connections can underlie the resulting understanding.
Conventional: A traffic signal communicates an instruction because its meaning has been established by agreement.
Rational or empirical: Smoke may lead one to infer fire as its cause, based on a known connection between effect and cause.
Natural: An involuntary cry or groan may reveal pain because it expresses a natural bodily condition.
The examples distinguish the grounds of indication. In real cases, context and alternative causes still matter when deciding exactly what a particular sign establishes.