Okay kiddo, a ghost sign is like a secret message from the past that is still there even though nobody uses it anymore. Do you know what a sign is? It's like a big picture with words on it that tells you what something is or where to go. A ghost sign is an old sign that was painted on a building a long time ago, but nobody has painted over it or taken it down. So you can still see it even though it's not being used anymore. It's called a ghost sign because it's like a ghost from the past that's still hanging around. People like to take pictures of ghost signs to remember what things looked like a long time ago.