SOUTH PORTLAND, Maine (AP) — The U.S. Coast Guard says someone has been stealing brass sound-signaling devices from buoys off the Maine coast — threatening the safety of mariners.

Coast Guard officials in South Portland said Thursday that the thefts pose a risk to public safety, as the brass gongs and bells produce sounds that help mariners navigate through poor visibility conditions. The Portland Press Herald reports tampering with aids to navigation is a federal offense punishable by fines of up to $25,000 per day or up to one year in prison.

The Coast Guard says anyone providing information leading to a conviction may be eligible to receive up to half the fine imposed by the court.

Coast Guard spokeswoman Lt. Chellsey Phillips says six buoys have been targeted over the last six months.