World's Fair yo-yos has been produced for a number of fairs, the biggest in 1939, with the New York World's Fair. This fair drew 45 million visitors, each taking home a World's Fair branded yo-yo as souvenir. At least 5 different yo-yos were produced for this specific fair.
Other World's Fairs also had yo-yos produced, among those the 1904 St. Louis World's Fair (with an iron bandalore) and the 1962 fair with a Space Seattlite Needle yo-yo.
These yo-yos are not related to the Worldsfair yo-yo produced by Forester.