WOODINVILLE, Wash. – Three seven-figure dream homes went up in flames early Monday in a Seattle suburb, apparently set by eco-terrorists who left a sign mocking the builders’ claims that the 4,000-plus-square-foot houses were environmentally friendly.

The sign – a sheet marked with spray paint – bore the initials ELF, for Earth Liberation Front, a loose collection of radical environmentalists that has claimed responsibility for dozens of attacks since the 1990s.

The sheriff’s office estimated that Monday’s pre-dawn fires did $7 million in damage to the “Street of Dreams,” a row of unoccupied, furnished luxury model homes where tens of thousands of visitors last summer eyed the latest in high-end housing, interior design and landscaping. Three homes were destroyed and two suffered smoke damage.

Crews removed incendiary devices found in the homes, Snohomish County District 7 Fire Chief Rick Eastman said. Later, however, Kelvin Crenshaw, special agent in charge of the Bureau of Alcohol, Tobacco and Firearms in Seattle, said there was no evidence such devices had been used.

The FBI was investigating the fires as a potential domestic terrorism act, said FBI spokesman Rich Kolko in Washington, D.C.

No injuries were reported in the fires, which began before dawn in the wooded subdivision and were still smoldering by midmorning.

The sign left behind said in red scraggly letters, “Built Green? Nope black!” and “McMansions in RCDs r not green,” a reference to rural cluster developments.

One alleged ELF activist is on trial in Tacoma in the 2001 firebombing of the University of Washington’s Center for Urban Horticulture. Investigators had no evidence linking the fires to the trial, Seattle FBI agent Fred Gutt said.

The homes that burned were between 4,200 and 4,750 square feet, are on sale at prices up to nearly $2 million.

One of the people involved in the project said the homes used “green” techniques such as water-pervious sidewalks, super-insulated walls and windows and products made with recycled materials, such as carpet pads.

Associated Press writer Lara Jakes Jordan in Washington, D.C., and Gene Johnson in Seattle contributed to this report.