3.5" double layer of die-cut cardboard marked "Copyright Fawcett Publications, Inc." From the 1940's. Front and back feature same image of Captain Marvel flying plus numerous lightning bolt accents. The cardboard is intended to be slightly flexed and then blown into on the mouthpiece end to produce the sound. These were issued with various imprints on the interior and this one has an illustration on how to hold the whistle plus text "Distributed By The Penny King Company, Pittsburgh #10, Pa." Cardboard is very lightly tanned on one side while the other side is close to Mint. First we've seen in about five years.