FAIR OAKS, Calif. -- Some Fair Oaks residents are concerned for their property after someone vandalized their vehicles, spraying them with letters associated with an eco-terrorism group that has recently been active in Northern California.

The residents' pick-up trucks and sport utility vehicles were spray-painted with the letters E.L.F., which may stand for Earth Liberation Front.

Keith Lott's Ford F150 was one of the pickup trucks that was tagged. He said he found "E.L.F." spray-painted on the tailgate of his vehicle Monday morning.

If the tagging is related to ELF, Lott believes he may have been targeted because his job is in construction equipment sales. His business is clearly visible on the side of the pickup truck.

"I know ELF is very much against development and construction in the Sacramento area," Lott said.

A neighbor's SUV was also tagged with E.L.F., according to authorities.

Investigators say it is still to early too tell if the latest vandalism is related to recent fire bombings or simply the work of vandals.

Ryan Lewis, 21, of Newcastle, is being charged in connection with three ELF-related fire bombings. Since he has been in custody, two other explosive devices have been planted in the area.