In auditory warning design the idea of the strength of the association between sound and referent has been pivotal. Research has proceeded via constructing classification systems of signal-referent associations and then testing predictions about ease of learning of different levels of signal-referent relation strength across and within different types of auditory signal (viz., speech, abstract sounds, and auditory icons). However, progress is hampered by terminological confusions and by neglect of the cognitive contribution (viz., learning) of the person or user. Drawing upon semiotics and cognitive psychology, the authors highlight the indexical (as opposed to iconic) nature of so-called auditory icons, and the authors identify the cogniser as an indispensable element in the tripartite nature of signification. Classifications that neglect this third element, defining signal-referent relation strength only dyadically, yield results confounded by learning; classifications that correctly include the triadic relation yield research predictions that are redundant. These limitations of the standard method of constructing and testing classification systems suggest that auditory warning design must take the cognitive contribution of the user into account at an earlier stage in the design process.