A signboard is a flat piece of wood, metal, or cardboard put up in a public place, with writing or a picture that tells people something — a shop name, a bus stop, a warning, a direction. It is a plain, physical word: you can point at the board itself hanging over a door or standing by a path. In everyday talk people often just say sign. Though actually, signboard keeps your eye on the object, the board, not only on the message. A painted name over a shop is a signboard; the words in a book are not.