A No Ghosts Sign is a sign that is typically placed in haunted places to ward off ghosts. Some signs may include a warning that ghosts are not welcome. There is no scientific evidence to support the claim that No Ghosts Signs actually work, but they remain a popular way to keep ghosts away. Some people believe that the signs' symbolism is enough to scare away ghosts, while others believe that the signs simply create a sense of psychological comfort. A No Ghosts Sign Sticker.