UPPER EAST SIDE, NY — When Rebecca Lamorte arrived at Carl Schurz Park on Wednesday, she almost missed the official-looking, red-and-white sign affixed to a post near the park's East 86th Street entrance.

"It didn't dawn on me right away until I stopped to read it," said Lamorte, one of the co-founders of the group Upper East Side for Black Lives Matter (UES4BLM), which has held nightly demonstrations against racism in the park since June.

When she examined it more closely, she realized it bore a startling message: "ABSOLUTELY NO PROTESTING ALLOWED."

"I was like, oh, this is an encroachment on our First Amendment right," she said. "So I immediately took a photo — I did what millennials do, I put it out on social."

Lamorte's tweet triggered a quick response from city agencies, who said the sign was not official, and from City Councilmember Ben Kallos, who represents the neighborhood.