Not a "supercar" agency (that I know of) but there is a story:
I noticed, when the light hits it just right, that the emblems and decals on the rear bumper of my Grand Prix have cooked "ghost images" into the chrome. You can actually read the text of the sticker that was placed there.
One of the stickers was from the selling dealership: Stevenson Pontiac in Ludington Michigan.
It was clear enough that I made a sketch and had some decals made up, emulating the same size and font. I don't know what the original colors were so I chose the colors somewhat randomly based on stickers from around here that I liked.
The dealership is gone but, appropriately enough, the building is still there and is now a small swap meet/flea market.
K