It is widely accepted that a sexual ornament can reveal quality because of the challenges associated with producing or bearing such traits. ~ Innes Cuthill et al
Animals horns and other traits of male dominance reflect fitness: good genes naturally, but more particularly the quality of early development, notably nutrition. Any developmental mechanism with hormonal sensitivity is reflected in the variable traits which demonstrate fitness. Hence, biological efficiency translates into honest communication by way of developmental physiology. Some things can’t be faked. Animal virility is one of those things.
Through honest communication many animals quickly gain accurate information about the fighting ability of an opponent, make a probabilistic determination, and terminate encounters they cannot win. Likewise for sexual selection, where honest signaling conveys economy of effort in choosing a mate.