Final answer:
Charles Peirce categorized signs into index, icon, and symbol: an index has a causal link, an icon resembles its object, and a symbol's meaning is culturally learned and arbitrary.
Step-by-step explanation:
Charles Peirce distinguished among the three types of signs - index, icon, and symbol - in semiotics, the study of signs and symbols and their use or interpretation. An index is a sign that has a direct, causal connection to the thing it signifies, such as smoke signifying fire. An icon resembles or imitates the thing it represents, like a portrait resembling the person it depicts. Lastly, a symbol has a meaning that is not related to its form and must be culturally learned, such as linguistic words or company logos; it is arbitrary and relies on convention.