Abstract: An illuminated sign panel adapted for mounting on the sides of vehicles such as trucks and having removable and replaceable sign display areas in the form of sheets of transparent or translucent materials. A sign display area may be composed of one sheet or several. The illumination is indirect and is designed to be supplied from behind the sign display area. The display panel is rigidly and fixedly mounted on the vehicle which can be an automobile, panel truck or truck trailer, for example.