Ostension is a common mode of communication based on a consensus, tacit or explicit, that links the things shown and the object at stake in the communication process (Eco, 1992). Different views of ostension have been developed through research in didactics conducted under the theory of didactic situations (Brousseau, 1998), studying the evolution of didactic situations in instruction. The role of signs in didactic transposition has also been studied through the notion of ostensives in the anthropological theory of didactics (Bosch & Chevallard, 1999). Our approach follows these research studies in a different way, retaining a semiotic view of ostension based on the links between icon, index, and symbol proposed by Peirce and interpreted by Conne (2008) in the field of research in didactics. Our work permits us to characterize didactic ostension as ostension of an object of knowledge for which the consensus must be explicit in the didactic situation. This need is a consequenc e of the symbolic character of language, and of the specific examples produced in this kind of communication. Thus the thesis of this article is that didactic ostension is itself a symbolic sign of the didactic transposition process.