WATERVILLE, Vt. – With its tidy brick farmhouse and adjacent red barn, Old Homestead Farm looks more like a New England postcard than a crime scene. But it’s one of the latest victims in a bizarre string of thefts.

Someone scaled the barn roof, possibly using climbing gear, and stole a copper-and-zinc weather vane that had flown from the 40-foot-high cupola for more than 150 years. The antique, which depicted a horse, was replaced with a cheap replica.

No one noticed until one day in June, when farm owner Elaine Thomas and her adult daughter were on a nearby hillside. The horse’s tail didn’t look right, Heather Thomas said.

Elaine Thomas looked, and was hit with a wave of shock. “I just screamed, ‘That’s not our horse,” Thomas said. “I knew instantly.”

The antique weather vane is among more than 20 that have been stolen in recent years in New England and New York.

“Those are just the reported cases,” said Sgt. John Flannigan, a spokesman for the Vermont State Police. “I just wonder how many of these may have occurred and may not have been reported to the authorities. They may not even know it.”

Weather vanes have become prized pieces of American folk art, routinely selling for $10,000 and up. One, which depicted a locomotive and had sat atop the Woonsocket, R.I., train station, sold earlier this month at auction for $1.2 million.

Some farmers are so concerned about thefts that they have removed their antique weather vanes and put up replicas.

The weather vane taken from Elaine and Dennis Thomas, fifth-generation farmers, “was our logo,” Elaine Thomas said. It was of a Morgan horse, a breed developed in Vermont two centuries ago that the couple raise.

“You wouldn’t think there’d be any crime out here, but there is,” Elaine Thomas said. “I just wish he’d taken the SUV, or a bicycle or a canoe. Things we could replace.”

It’s unclear whether recent thefts of weather vanes are related. Since January 2005, at least three have been reported stolen in Massachusetts, one in York, Maine, and at least one in Concord, N.H., where police recovered a weather vane that had been transported to Florida.

Concord police are working with the U.S. Postal Inspection Service on another case involving a stolen weather vane, but officials refused to discuss it, saying it was an active investigation.

Theories abound about who may be responsible for the thefts.

“Is it someone who’s there to do work on a house, some kind of repair work? Or is it people who are targeting these weather vanes? That’s the mystery,” Flannigan said.

Thieves often erect replacements when they steal weather vanes – and that’s not an easy job, according to antiques expert Kathy Greer, editor of Laconia, N.H.,-based “Unravel the Gavel,” an antiques newspaper.

“To put one of these weather vanes up takes more than one person,” she said. “Some of them, I would guess, have to weigh a couple hundred pounds. It’s just not something you’re going to stick under your arm.”

Jean Burks, senior curator of the Shelburne Museum in Shelburne, which has an extensive collection of weather vanes, said stolen ones often turn up for sale in antiques magazines. But dealers are leery about buying ones they believe may have been stolen, she said.

“It’s a pretty tight network and people are aware of what’s been stolen. It’s not going to go far. I’m sure [the Thomases will] get it back the minute it starts changing hands … to some professional dealer,” said Burks.