Any content-word in the language is a sign, being a spoken or written vehicle for an immaterial meaning that refers to some experience. A symbol is a sign which has further layers of meaning. In other words, a symbol means more than it literally says. Notice that a symbol can have more than one layer of further meaning. One person may have strong affection for dogs while another person may fear them intensely.
Lions suggest deity in a variety of cultures, for instance.
Trying to discern and express the universal meaning of a symbol is tricky. Symbols and Interpretation Meaning precedes explanation. In interpreting literature, it is important to remember that a poem or a short story means more than the writer consciously intended. It can have this surplus of meaning because of the way language works. Neither writer nor reader is in control of these associations.