What signs were used in world war 1?

During World War I, various signs were used for communication and signaling on the battlefield. These included flags, known as signal flags, which conveyed messages between ships and units, as well as semaphore systems and visual signals. Additionally, posters with slogans and Propaganda were widely used to recruit soldiers and promote war efforts. Color-coded maps and trench signs also played a crucial role in navigation and identifying different units and areas.