Aposematic coloration is commonly considered to signal unpalatability, yet animals advertise malodour, spines, and weaponry as well as toxins, some of which can be seen at a distance whereas others are hidden from predators. Separating defences into overt and covert categories in this way and whether they act before, during contact, or following ingestion generates new insights into the evolution of aposematism. Signals drawing attention to overt defences are difficult to fake whereas signals advertising covert defences can deceive would-be predators, and those acting later in the predatory sequence are more likely to be dishonest. These two orthogonal defence categorizations help to frame where dishonest signalling occurs in nature, set limits on deception by dishonest Batesian mimics, and prompt new questions.