There are numerous synonyms that can be used in place of the phrase "ancient symbol". For instance, an "archaic emblem" is a term that can be used to describe a symbol that has existed for many years and is representative of an older period. The phrase "timeless icon" is also a useful synonym, as it conveys the idea that the symbol has been significant throughout history and remains relevant today. Other options include "antiquated insignia," "time-honored mark," and "ancestral glyph." Depending on the context, any of these phrases could be used in place of "ancient symbol" to add some variety and depth to the language.