Bull's horns are a common heraldic element, painted on shields and depicted on helms as decorative crests.
"BULL'S HORNS: Denotes strength, power and fortitude; horns were used also as divine power. The bull's horns represented fertility of the earth, growth, and generation, analogous to spring, when the earth is fertile and everything is growing abundantly. Bulls were revered as the masculine counterpart to goddesses in the ancient Mediterranean." -- Armorial Gold