A fertility symbol was any object or image that stood for reproduction.
A horga'hn was a Risian fertility symbol. (TNG: "Captain's Holiday"; DS9: "Let He Who Is Without Sin...")
In 2373, Kes and Neelix debated the meaning of a symbol they found in the Nechisti shrine. Neelix speculated that it might be a fertility symbol, while Kes thought it might be a blessing for good luck or wisdom. Neelix then further suggested it could stand for happiness or love. (VOY: "Sacred Ground")
Fertility totem of Mavok Prime