Throughout the decades, the 215 area code has become an instant cultural identifier for the Philadelphia region, writes Max Marin for Billy Penn.

Philadelphia and its surroundings have been associated with an area code since 1947, when AT&T unified the dialing system nationwide. Since then, it has been used countless times in songs, artwork, and even as the title of a magazine.

In the 1990s, rap music further helped codify the numbers as part of Philadelphia’s identity. Among others, “The 215” became the calling sign for The Roots. It appears in several of the band’s songs, including “Respond/React,” the opening song of their third album, Illadelph Halflife.

The area code has also been used in other aspects of branding as well. The Pennsylvania business registry lists more than 200 entities starting with “215,” and an additional 10 with “two one five.”

Even a late-season episode of The Fresh Prince of Bel-Air threw in an Easter Egg nod to the number: The hospital room in which Will Smith’s character stayed after being injured during an ATM holdup was 215.

Read more about the 215 area code at Billy Penn.