I seem to recall back in the 80's there was a styling trend for reflective panels with the name of the car on it called a 'backflash'. Like the Heckblendes they usually went between the lights on, mainly on Astras and XR3's. And I remember you could get one for the Golf which fitted on the panel below the tailgate/lights.
If I'm right it's rare, since few people would have fitted one. I'd recommend you remove it very carefully as they used strong adhesive pads, then snap it in half and burn it.