Among many other contradictions of the Great War, one has to consider the fact that WWI is probably the first historical global event where the representation of things was systematically and intrinsically part of the conflict itself. And representation needs words, links between signifier and signified which appear to be broken when reading diaries, reports from the front. It is impossible to find words to describe a horror that was unnamable, to find words to say and represent something that was not possible to represent.In considering the communicative essence of posters, a mixture of speech and writing, Austin’s (1962) notion of “illocutionary force” and “perlocutionary act or effect” are powerful agents in reconceptualising the way language relates to the world. This chapter investigates how perlocutionary force, together with the idea of pre-texts, was used in war posters to name the unnameable.