The use established by Charles Peirce is widely accepted by modern semioticians to denote a specific type of sign or sign function in which the sign vehicle provides its object through an actual or physical connection.
For example, the wind vane is an indexical sign, as it shows the direction of the wind through a current relationship between the wind and itself.
According to Peirce, signs can refer to their objects in three different ways:
- based on similarity or resemblance (iconic signs)
- of an actual or physical relationship (indexes)
or - based on habit, whether innate or acquired (symbols).
Indexes (also called indexical signs) are those signs that the sign vehicle is currently or physically associated with its object.
