A symbol is something that stands for something else. The term symbol is one of many people use to talk about communication, including verbal and nonverbal communication. Another, more general term is sign. While some scholars use these and other terms in a rigorous way to analyze communication, it helps to talk about them more generally at first.
Symbols are not the only mode of communication. We can make a provisional distinction between at least three kinds of signs
This is Charles Sanders Peirce's trichotomy of signs: index, icon, and symbol respectively (Atkin 2013).
Yet, all signs in the real world have a mix of all three kinds of sign. For a cultural anthropologist, it is especially important to see the symbolic aspect in every kind of communication. Clearly, when we think of culture in a Boasian sense, we would also conclude that people acquire a vast number of conventional signs (symbols), just as they acquire a vast number of words for ideas when they learn a language. People also have to learn to read natural signs in conventional ways. Some of this is by gaining specific knowledge. For instance Auhelawa gardeners have to learn to read the falling of rosewood leaves as a sign of a new phase of yam gardening. The falling leaves are a natural sign of a seasonal change. The symbolic connection between leaves and yam harvesting is learned. Other kinds of apparently natural signs have one conventional meaning in one culture and another in another culture, and people have to acquire their culture's conventional way of reading them. In Auhelawa, people abstain from washing and wearing clean clothes when they are in mourning for a relative who belongs to another matrilineage (e.g. the wife and children of a man who dies, or the husband of a woman who dies). There is an indexical (natural) meaning of their dirty appearance in the sense that it is a direct outcome of their observance of a prohibition. Auhelawa people also read this index in a conventional way as a symbol of ve'ahihi (respect) for the matrilineal relatives of the deceased.
A Boasian cultural anthropologist would emphasize the way that the symbolic aspects of signs determines how we read and understand the world. Think about police tape around a crime scene.
In some way, the space of crime scene is communicated by a natural sign: the tape marks the boundary. But imagine this from a purely etic perspective. Imagine being an alien from outer space. How do you know that this line should not be crossed? What's to say that it's not a finish line or a decorative ribbon? The markings on the tape are read symbolically, and would only make sense in an emic perspective. The space of the crime scene is visible to someone with this emic perspective. In that sense also, crime scene is an emic category within the cultural worldview of New South Wales.
Atkin, Albert. 2013. “Peirce’s Theory of Signs.” In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Summer 2013. Metaphysics Research Lab, Stanford University. https://plato.stanford.edu/archives/sum2013/entries/peirce-semiotics/.
“NSW Police Tape.” 2019. ABC News. May 21, 2019. https://www.abc.net.au/news/2019-05-21/police-tape-generic-nsw/11132618.