When looking for symbols in culture, do a keyword search that includes your symbol as well as the word "symbol" with a truncation device at the end (*). For instance:
The asterisk will tell the database to include results containing the word symbol, symbols, symbolism, symbolic, symbology, etc.
Also try the keywords semiology and semiotics (the study of signs and symbols and their use or interpretation).
Subject headings are also important! Try typing DE "Signs & symbols" in the first keyword box and the symbol of your choice (ie, circles) in the second to get only articles pertaining to circles as symbols.