In 1990s Washington, being known as a “friend of Bill” meant you were someone like Vernon Jordan or Mark Penn—a member of Bill Clinton’s inner circle. But long before Bill Clinton, there was Bill Wilson. And this Bill had a whole lot more friends.

Wilson was a savage drunk for nearly 20 years. But, by 1935, he had founded what would become one of the most successful social experiments of all time: Alcoholics Anonymous. (Guess which Bill ranked among Time’s 100 Most Influential People of the 20th Century?) Anonymity was particularly important in the ’30s, when overt drunkenness was likely to land you in an insane asylum. Over the years, “friendship” with Bill has become a stand-in for sobriety—a useful secret handshake between addicts navigating an often-judgmental straight world. It can be a subtle clue in obituaries (my grandfather was “an avid woodcarver [and] a friend of Bill W.’s for 24 years”) or an urgent signal over an airport P.A. system from a tempted addict in search of an ally (Paging any friends of Bill W. in the terminal, please meet Raquel J. at Starbucks). Should I see you sipping OJ at an office party, I might say: “I think we have a mutual friend. Do you know Bill W.?”

This code, today a quaint bit of subterfuge in a reveal-it-all Internet age, remains a useful calling card—allowing you to circumvent the pesky demands of anonymity while respecting them at the same time. Of course, by explaining the term, I’ve just violated its central purpose.

Sacha Z. Scoblic is a contributing editor at The New Republic, the author of Unwasted: My Lush Sobriety, and a Carter fellow for mental health journalism. Follow @sachaZscoblic.