This small essay on the luminous sign in the twentieth century is part of a vast program of studies seeking to highlight an anthropology of contemporary writing. A strong conviction underpins this collective inquiry: there is not only a graphic reason but a power of writing that gives our lives ways to think and act. The search for these microdevices of writing, sometimes ephemeral, often neglected by research, allows, we believe, to apprehend an unexplored dimension of our ways of doing things. With the history of the luminous signs unfolds hollow parts of our contemporary history. That of an invention, its actors, a small business but also a twentieth century imagination. Demonstrating, if need be, that there are no incidental or anecdotal objects in history.