Since for most of arcade gaming's heyday graphics weren't exactly easy on the eye, to lure customers in companies often had to rely on artwork to make a sale.
The biggest, grandest works were reserved for the side of the cabinet, but since they usually weren't seen (with machines stacked side-by-side), it was the "marquee" that helped make a game stand out. And as you're about to see, that meant there was usually some badass art on them.
The marquee was the piece of paper at the top of the cabinet that slid into the "hood" of an arcade machine, and would be backlit when the cabinet was powered up. On "themed" cabinets, as in ones that had custom-painted sides, that theme would carry on into the marquee, helping create one enormous piece of advertising and branding.
They were also useful, however, on cabinets that could have their games swapped out, as in those cases the art on the marquee was usually the only thing identifying the machine through the crowd of an arcade.
If any of it takes your fancy - and there's something wrong with you if at least one of them doesn't - emdkay sell a bunch of them.