WOODINVILLE, Wash. — Fires gutted three multimillion-dollar model homes in a Seattle suburb on Monday, and authorities found a sign purportedly left by eco-terrorists that mocks claims that the homes were environmentally friendly.

"Built Green? Nope black!" said the spray-painted sign that bore the initials of the radical environmental group Earth Liberation Front.

Crews removed explosive devices found in the homes, said Fire Chief Rick Eastman of Snohomish County District 7. 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. The sheriff's office estimated damage at $7 million. In addition to the three homes destroyed, two sustained smoke damage.

The houses burned as a federal jury in Tacoma was about to resume deliberations in the case of an alleged ELF activist, Briana Waters. Waters could face at least 35 years if convicted of helping to firebomb the University of Washington's Center for Urban Horticulture in 2001.

The fires started at the "Street of Dreams," an annual real-estate promotion in the region. The cluster of unoccupied, furnished luxury model homes are a way for developers to show off the latest in high-end housing, interior design and landscaping. The homes are first opened for tours, and later sold.

The homes, none of which had been purchased, are in a development near the headwaters of Bear Creek, which is home to endangered chinook salmon. Opponents had questioned whether the luxury homes could pollute the creek and an aquifer that is a drinking water source, and whether enough was done to protect nearby wetlands.

The sign, a sheet with red scraggly letters, said "McMansions in RCDs r not green," a reference to rural cluster developments.

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.

"It's very disappointing to take a situation where we're tying to promote good building practices — Built Green practices — and that it's destroyed," said Doug Barnes, the Northwest division president of Centex Homes in Kirkland.

Advertising for the most recent Street of Dreams show focused on the earth-friendly aspects of the homes, which were smaller than some of the huge houses featured in years past. Although the homes featured energy efficient appliances, water-saving toilets and nontoxic paint, they also included three- and four-car garages, and luxuries such as home theaters, spas and bars.

The homes that burned were between 4,200 and 4,750 square feet, with prices as high as nearly $2 million.

The Earth Liberation Front is a loose collection of radical environmentalists known for trying to cause economic damage to companies or organizations that, in its opinion, harm the environment. The group has no organized structure or leadership; typically, autonomous cells of activists take "direct actions" such as arsons and claim responsibility on behalf of ELF.

In 2005, federal authorities charged more than a dozen people involved in an ELF cell known as "the Family" and centered near Olympia, Wash., and Eugene, Ore. The group was responsible for at least 17 fires around the West from 1996 to 2001 — most notoriously, the 1998 destruction of the Vail Ski Resort in Colorado, a fire that caused $12 million in damage.

Waters, a 32-year-old violin teacher from Oakland, Calif., is accused of serving as a lookout while her friends planted a devastating firebomb at the UW's horticulture center in 2001, causing $7 million in damages. The horticulture center was targeted because the ELF activists mistakenly believed researchers there were genetically engineering trees, investigators said.

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