That is a cool Detroit Chevrolet license plate frame (especially since I live an hour north of Detroit). Just an FYI, Mack and Gratiot are streets in Detroit which intersect, which was probably the location of the long-gone Chevrolet dealership that your frame is from. It is literally about 500 feet from the Faygo soda plant. Faygo is a Michigan made local favorite, not sure how many states they export to.
There is also a building with numerous layers of advertising painted on the side. One layer of paint looks like “Chevrolet”, because it starts with a ‘C’ and has a ‘let’ at the end, it might have said something else, because there is another ‘L’ right after the ‘let’ but the font is definitely correct. Who knows, it could’ve been the advertisement from your dealership!