In early July, tickets went on sale for the Saatchi Gallery's 2016 show "Exhibitionism," two full floors of posters, costumes and other iconography belonging to the Rolling Stones. London buzzed about the show for weeks, but when Saatchi tried to place its advertising posters in the Underground, transit officials turned it down flat. The reason? The band's famous logo of a licking tongue had been applied to … a photo of a woman's crotch.

The moment wasn't just a fitting testament to the band (the Stones have always pushed social and sexual boundaries) but to its chosen emblem. Its original, clunky name is the "Tongue and Lips" logo, which some have shortened to just "Hot Lips." Call it what you want, it became the most famous icon in rock—and still is now, as the Stones kick off their ZIP Code Tour.

"It's really the most evocative logo of any band," said Mash Bonigala, who runs image consulting firm Spellbrand. "By distilling the essence of the band into one single visual reference, the designer was able to create a logo that worked superbly well for 50 years."

Branding a rock band with a signature badge was a novel idea in 1969 when Mick Jagger called on London's Royal College of Art in search of a student to create some visual assets for his band's next album. The Stones' front man liked the work of 24-year-old John Pasche, who accepted £50 (about $77) to draw up a logo. The story goes that Jagger wanted a likeness of Kali, the Hindu goddess of everlasting energy. And while Kali does boast a large mouth with her tongue sticking out, Pasche found greater inspiration in Jagger himself. "I went into this sort of wood-paneled boardroom and there he was," Pasche said. "Face-to-face with him, the first thing you were aware of was the size of his lips and mouth."

Having debuted on 1971's Sticky Fingers LP, Hot Lips was so popular that the band never retired it. And it's stayed relevant for all the same reasons the Stones have. Both are about sex, defiance and Jagger's big mouth. Pasche's legendary rendering is proof of the adage that something that isn't broken doesn't need to be fixed.

"If a good logo is going to endure, it needs to be appropriate," adds U.K. designer David Airey, author of the book Logo Design Love, "and the sexiness associated with red lips is fitting for legends of rock 'n' roll."

Speaking of appropriate, Saatchi did wind up getting its ads into the London Tube, by moving up the Tongue and Lips logo from the crotch to the navel instead.

This story first appeared in the July 20 issue of Adweek magazine. Click here to subscribe.