The loadedChanged(event, loaded) method can be overrided to get notified when a sign matching this sign action is loaded or unloaded on the server. A sign is loaded when placed, or when a chunk loads with the sign in it. A sign is unloaded when destroyed, or when a chunk unloads with the sign in it. Be careful not to load or unload chunks in this method. This is a useful method to cache data in memory while the sign is in use.