I think this is called “Aposematism”:

Aposematism is the advertising by an animal, whether terrestrial or marine, to potential predators that it is not worth attacking or eating.[1] This unprofitability may consist of any defenses which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature. These advertising signals may take the form of conspicuous coloration, sounds, odours,[2] or other perceivable characteristics. Aposematic signals are beneficial for both predator and prey, since both avoid potential harm.