New Yorkers lucky enough to own a building with one of street artist Banksy's newest works have taken to hiring security guards. And with good reason -- similar works in England have sold for more than $1 million.

In the South Bronx, building owner David Damaghi hired two guards to protect a Banksy work depicting a small boy spray painting while a butler held his paint cans, the web site Gothamist reported. In the Red Hook section of Brooklyn, a building owner hired a guard after a different grafiti artist painted his own tag under a Banksy red balloon. And in Williamsburg, owners installed a pull-down metal gate and hired guards to protect a piece after it was almost defaced.

In addition to the dangers of defacement, the works are likely quite valuable. Banksy's outdoor paintings, cut from walls, doors and the sides of buildings have sold for over $1 million. Just in June, a mural of a boy sewing a Union Jack flag, known as "Slave Labour," sold for $1.1 million at a private auction. The work had been removed from the wall of local retail shop in North London in February.

Even without an auction, having Banksy's work visible on a building can lift its value. After Banksy painted a huge rat on the side of boarded up Liverpool pub in 2008, the building's value increased by an estimated $800,000.

Sales of Banksy's outdoor art have been controversial. While a group known as Pest Control validates the authenticity of Banksy's gallery art, it does not opine on street works. Major auction houses like Christie's won't sell alleged Banksy works lacking the validation.

Read More: Yahoo! News

Photo Credit: Getty Images/Michael Loccisano