NEW YORK (CBSNewYork) — A new problem has emerged for postal workers and the neighborhoods they serve; thieves are on the lookout for the carts they carry around that are filled with mail.

Residents in one neighborhood say they were made aware that some of their mail may be missing.

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While postal workers circle their routes with the carts, thieves are keeping a close eye for moments they’re left alone while the carriers are inside delivering the mail.

Randy Kornish of Murray Hill says it happened outside his building just weeks ago. They problem, he says, is that they can’t bring them inside.

“Some doormen don’t want it and some of them have to go upstairs,” he told CBS2’s Erin Logan.

Sources tell CBS2 the thieves sift through the carts looking for specific pieces of mail. There have been 16 cases reported since January. In one of them, the suspect was dressed up as a postal worker.

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In Gramercy Park, the Hoffmans say they witnessed their postal worker very upset.

“There was a UPS worker or FedEx worker here and she said ‘Did you see my cart? My cart is missing’,”  Dorothy said. “She couldn’t believe it.”

Dorothy says the entire building was notified that they may be missing mail. One postal worker told police he witnessed a man take off with his cart. The District Attorney’s office says it happened in November outside an East 77th Street building. The postal worker followed him a short distance, where the man ditched the cart.

He was sentenced to 60 days in jail.

“I guess 60 days in jail is good, but it should be discouraged,” Hoffman said said. “If they’re using it to further additional crimes like identity theft it’s more serious.”

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Meanwhile, Hoffman and Kornish are hoping the cart thieves know police are looking for them.