Last month, Vanessa Thompson stepped outside the juice bar where she works on Nostrand Avenue in Brooklyn and noticed a green and white sticker on a light pole. She leaned in for a closer look.

“John van Nostrand was a slave owner,” it said. “According to the US census in 1790, the (Van) Nostrands owned 6 people.”

Ms. Thompson, who is Black, was dumbfounded. “I didn’t even know anything about that,” she said. “He could’ve owned me.”

The sticker was partly the brainchild of Elsa Eli Waithe, 33, a comedian living in Crown Heights, Brooklyn, who, along with two collaborators, has been on a mission to let New Yorkers know that a good number of the city’s streets, subway stations and neighborhoods are named after enslavers.

The project was inspired in part by a talk between Mx. Waithe, who is Black and grew up in Norfolk, Va., and a white friend about a Confederate monument in Portsmouth, Va., that was dismantled last August. Mx. Waithe recalled the friend’s dismissing the statue as a Southern issue, a regional affront.

But just a few months before, while scrolling through social media, Mx. Waithe had stumbled upon records from the nation’s first census in 1790, which listed well-known New York families like the Leffertses, the Boerums and the Nostrands. To the right of those names was another category: “slaves.”

According to the census, the Lefferts family enslaved 87 Black people throughout New York City (Prospect Lefferts Gardens and an avenue in that Brooklyn neighborhood were named after them). The Boerums owned 14 slaves (the neighborhood Boerum Hill is named for them). And the Nostrands (of the eight-mile-long Nostrand Avenue), enslaved 23 people (this number would nearly double by the beginning of the 19th century).