Burger King had two promotions for THE EMPIRE STRIKES BACK. The first ran for a month and a half that summer, and was called the "Everybody Wins Game," because you received a scratch-off card with purchase, and, as the name implied, you would win something. The most common prize was the best one, in the long run: a strip of Star Wars trading cards!
A set of 36 cards was made, in strips of 3 cards, which were perforated. Six strips featured images from Star Wars, and six featured the new film, which added up to 18 cards from each movie. Ironically, the game-piece card is probably the "rarest" card associated with the set, because over 21 million strips of trading cards were given out, but lots of people didn't think to keep the game piece, which was the size of a trading card, and featured art of an X-Wing. It was also the entry blank for mailing in your entry, so many probably were used for that purpose as well.
As you can see above, the backs of the cards were generic, and unnumbered. The only change between cards was the logo, showing you which film the card was from, as if you needed to know.
Here are the twelve strips of trading cards. I had a pile of these as a kid, but was lucky enough to acquire an intact set from a dealer many years ago: