Both verbal and nonverbal signs can work through three different kinds of connection: convention (waḍʿ), nature (ṭabʿ), and reason (ʿaql).
Conventional: a meaning is assigned or agreed upon, as with a person's name.
Natural: a condition naturally produces an expression, as when pain evokes a cry.
Rational: the mind infers something from an effect or a necessary connection, such as a sound indicating a sound-producing source.
What matters is the basis of the connection, not merely its outward form.