From my 1979 Turbo Sport Coupe... I know I don't have the rear of my old car pictured, but I do remember it only having a 'Buick' badge of the passenger side of the trunk. Also, the Sport Coupe emblems were on the side, nearthe door of each front fender.
Here are the only pictures I could find of the car to scan.
1979 Buick Regal Sport Coupe (Turbo) - a set on Flickr
I hope this helps.
Best,
Eric McCann
Germantown, WI