Oak Creek - Police investigating the vandalism of a Bush-Cheney campaign sign have tracked a license plate to a rental car linked to door-to-door canvassers hired by a vendor working on behalf of the Sierra Club.

Officials for the environmental group, which nationally endorsed Democrat Sen. John Kerry for president in May, said the individuals believed to be involved in the vandalism were dismissed immediately by the vendor, Field Works.

Joyce Harms, the team leader for the Sierra Club's Environmental Voter Education Campaign in Milwaukee, said the group is working to provide voters information on the environmental records of the two presidential candidates.

Police Chief Thomas Bauer said company officials are cooperating with the investigation and the individuals believed to be involved have yet to be interviewed. He said the campaign sign was damaged on Aug. 30 but was not torn down. A manager of a local store obtained a license plate number and reported the incident to police, Bauer said.