[Mr70]

Magic Mirror was the new acrylic lacquer paint that started on all GM cars for the 1959 model year,though some '58s had been painted with it as a test.
As has been said,your decal can't be any earlier than '64 because that particular logo didn't come out until then.
I've seen that decal once before and suspect it was part of a program for GM dealers to apply some kind of sealant or special polish,like Blue Coral.
...It's possible that decal is Canadian.