How does an index point to the thing it represents?

In the study of semiotics, an index does not point to its referent through resemblance or arbitrary convention. Instead, it functions by being directly associated with the thing it represents.1

As defined by the philosopher Charles Sanders Peirce, an index maintains a factual or causal connection to its object. A classic example is smoke, which serves as an index of fire because the presence of smoke is physically linked to the occurrence of fire. Unlike an icon, which mimics its referent, or a symbol, which relies on social agreement, the indexical sign is grounded in an existential or experiential relationship with the reality it denotes.1