BLUF: There are no "brush strokes" on factory manufactured pinball machine, even as far back as the 1940s.
This is private owner aftermarket "improvement".
Operators did not do it, because they did not care.
Understand that removing this extra layer of non-factory coating (most likely polyurethane, but I would personally take a sample and get it tested) with basic home methods, may break the factory lacquer beneath the coating cause layer peeling, and paint loss within the cracks.
Start with denatured alcohol (isopropyl alcohol won't help your cause, because it will not remove anything properly), and a soft terry cloth rag, watch the rag VERY carefully in a corner or a part hidden from basic view. Do not use heavier caustic solvents or you will liquify the extra coating, the original lacquer, and original paint into a gummy hot mess. This could destroy the playfield at worst case, and and best case be hell to try and clean up.