Images make a sign more striking

They draw the eye in a way that text sometimes doesn’t. We humans are visual animals and our eyes pick up on anything that looks interesting or unusual. In other words, adding an image to a sign makes it more likely that the sign will be noticed in the first place. Remember we all adhere to warning signs when driving, and signs that give us direction to ensure we remain within the law, a no smoking sign for example. Most of these have no words at all.