[Mr70]

Those are cool specific GM in house plates.
They used that type throughout many a photo over the years,before & after that.
Used as a source to document the Mfr./year a model was in their studio field photographs.
C stood for Communication,meaning their intended designated reference source like Centrals i.e promotional press,,and the 1 for Chevrolet..As opposed to Buick-Olds-Pontiac.
They were made out ot the thinnest tin back then,as they were obviously dated and disposed of once the next year came along.
I think I saw Ausleys or Ted Williams selling these repopped once back in the 1980's,but I don't think they were embossed like the originals were.
I've been waiting for an original for awhile now,as there are a few retired exec./techs who claim to have some.