On April 21, 1973, Tony Orlando and Dawn's “Tie a Yellow Ribbon Round the Ole Oak Tree,” tops the U.S. pop charts. The yellow ribbon has long been a symbol of support for absent or missing loved ones, but this song turned the tradition into a cultural phenomenon.

There are some who believe that the tradition of the yellow ribbon dates back as far as the Civil War era, when a yellow ribbon in a woman’s hair indicated that she was “taken” by a man who was absent due to service in the United States Army Cavalry. But research by professional folklorists has found no evidence to support that story. The Library of Congress itself traces the cultural ubiquity of this powerful symbol to the 1973 song.

“Tie a Yellow Ribbon” was a massive international hit, holding the top spot on both the U.S. and U.K. charts for four consecutive weeks and earning upwards of 3 million radio plays in 1973. It was sung from the perspective of a man returning home after three years in prison and looking anxiously for an agreed-upon sign that the woman he loves would welcome his return. Songwriters Irwin Levine and L. Russell Brown got the idea for the song from a story they’d heard while in the Army. New York newspaper columnist Pete Hamill sued Levine and Brown for copyright infringement because he believed they took the idea from a 1971 column of his relating a very similar story as fact. Hamill dropped his suit, however, when researchers uncovered multiple versions of the same general tale dating back at least as far as the 1950s. “Probably the story is one of these mysterious bits of folklore that emerge from the national subconscious to be told anew in one form or another,” Hamill said at the time. To use a more familiar term, it was an urban legend.

Fast-forward to January 1981, when the Library of Congress was inundated by press inquiries over the historical roots of the yellow ribbon. What prompted the sudden interest in the origins of the “tradition” was the spontaneous appearance all around the country of yellow ribbons welcoming the U.S. hostages home after 444 days in captivity in Iran. The Library’s experts heard assertions of connections to the 1949 John Wayne film She Wore a Yellow Ribbon, and they found a 1917 song called “Round Her Neck She Wears a Yeller Ribbon (For her Lover Who Is Fur, Fur Away),” but they found no actual evidence of anyone ever actually wearing yellow ribbons or tying them to trees, lampposts, etc.

Instead, the Library of Congress ruled that the most compelling evidence explaining the origin of the yellow-ribbon “tradition” was to be found in a television interview with Penelope Laingen, wife of the U.S. Chargé d’Affaires in Tehran, whose ribbon-bedecked Maryland home appears to have started the trend in 1981. “It just came to me,” she said, “to give people something to do, rather than throw dog food at Iranians. I said, ‘Why don’t they tie a yellow ribbon around an old oak tree.’ That’s how it started.” Her reported inspiration: the Tony Orlando song that reached #1 in April 1973.