WOODINVILLE, Wash. -- The FBI says it's investigating the "Street of Dreams" home fires near Woodinville as a potential domestic terrorism act.

Four large homes burned early Monday morning at the luxury model home development north of Woodinville, and a Snohomish County fire chief, Rick Eastman, said a sign saying ELF was left at the scene.

Eastman told KIRO 7 Eyewitness News that firefighters arrived to find one home engulfed in flames. Two other homes were burning and a fourth home was smoking.

An incendiary device was left in each home, firefighters said. A total of five devices were found. A device in one home apparently didn’t go off.

He said a passerby heard explosions at about 5:15 a.m. that sounded like gunshots.

KIRO 7 Eyewitness News reporter Michelle Millman said a sheet on a fence near one of the homes was spray-painted with the words: "Built Green? Nope black! McMansions in RCDs r not green. ELF." Chopper 7 showed video of investigators packing up the sign as evidence.

The ELF, or Earth Liberation Front, is a loosely organized collection of radical environmentalists authorities say is responsible for other arsons in the Northwest.

A woman is currently trial in Tacoma for a suspected ELF fire at the University of Washington in 2001. Briana Waters, a 32-year-old violin teacher, is accused of serving as a lookout while her friends planted a devastating fire bomb.

The homes were built last summer as part of the "Street of Dreams" project, an annual showcase of luxury homes in the Seattle area. The latest development is off Highway 522 at Echo Lake Drive.

Snohomish County sheriff's spokeswoman Rebecca Hover said the fires are being investigated by the Puget Sound Joint Terrorism Task force of FBI and ATF agents and county authorities.

Hover said the damage from the fires is estimated at $7 million. No one was hurt in the three-alarm fire.

The Building Industry Association of Washington is offering up to $100,000 for the identification of and information leading to the arrest and conviction of individuals responsible for arsons on homes claimed by ELF.

Anyone with information regarding possible ELF-related activities is asked to contact the FBI's Joint Terrorism Task Force at 206-622-0460.