Sticking it into Google says its the OE fit in a Brava, made by Grundig. The pictures of the front face do not show the model number.
So, if the model number is known, either it has been out of the vehicle, or the owner has the instruction book, which may show the model number.
Usual reason for a single digit display is that it is waiting for its security code to be input. That would be so if it had been removed from the vehicle, or was a replacement from another vehicle. Can also happen if the battery has been disconnected. Most units now are coded to the car, and will not need this code if used in its original vehicle. Older units often needed the code, so this could be the issue here. Once again, we don't get the full story.
Look in the handbook for the security code input section.