History The numbers on the Roadster 537B

We see this car every time we log on, and I never get tired of looking at it. Is it the Robert Stack car? When and where was the photo taken? The numbers are on artboard, maybe aluminum sheet and taped to the car, why? White shoe polish not good enough, or is is some aero experiment? I've looked at that photo for years, time I asked.
Bob

 

I saw something a while back that talked of the numbers, trying to recall where. JW

 

ask @Ryan

 

Buck Davis at Bonneville 1951

 

Thank you Jimmy.

 

If you have ever had shoe polish on paint on your car sit out in the sun for a while you pretty well have to polish the paint to get the ghost images of the letters or numbers off. It doesn't go away with just washing the car and that may be their reasoning for using the sheets of what ever with the numbers on it as tape residue was easier to deal with than what the shoe polish did to it.