This “Official Superman Club Member” pinback button was made by Button World Manufacturing in 1966. This pin measures about 3-1/2″ in diameter and features a great stock art image of Superman. (Darned if I can ID the artist, but I recognize all the art from a Superman slick sheet of the period.) It was sold in a plastic bag with an illustrated header card. Button World Manufacturing held the license for Marvel Comics character buttons in addition to DC’s Superman and Batman, and produced over a dozen different character pins including Green Lantern, Wonder Woman, Aquaman, Hawkman, Spider-man, Captain America, Thor, Daredevil, Hulk, Iron Man, and Sub-mariner. You can see some of the other pins they offered here.
These Superman pins aren’t difficult to find loose, but i hesitate to buy on that way because there have been bootlegs. It’s harder to find them in the original package.