On a stroll through the busy streets of Jackson Heights, Queens, Sahadev Poudel kept gesturing at the ground with disgust. He stopped on the sidewalks in front of sari boutiques and Indian grocery stores, pointing out stains that looked like dried blood.

“It’s all over the place,” said Mr. Poudel, 33, who immigrated from Nepal in 2004. “This is completely bad behavior that we brought from our hometown.”

The sidewalks of New York have long been blotted by black blobs where chewing gum met its demise. But the reddish-brown splotches that trouble Mr. Poudel are seemingly unique to the 74th Street commercial district, and they are causing friction among the South Asians who eat, work and shop there.

These are the marks of paan.

At a dollar each, paan has become a popular after-dinner treat in Jackson Heights. It is made by folding dried fruits, nuts and pastes into a betel leaf, a member of the pepper family. Some people like a sweet type of paan with candy-coated fennel seeds and rose petal preserves, chomping on it to freshen their breath or swallowing it to help digestion. Others go for paan with cured tobacco, despite warnings about blackened gums and oral cancer.