The growing problem was causing alarm on State Highway 1 between Milton and Dunedin.
Acting Senior Sergeant Murray Smith, of Dunedin, said the danger, especially on busy State Highway 1 and with high-powered rifles, was not simply that bullets went through signs, but where they ended up.
Shots could travel "quite a distance" and could ricochet.
Despite the difficulty of "tracing and tracking" offenders, Snr Sgt Smith appealed to the public to contact police at any time if they heard or saw guns fired on roadsides.
He reminded gun owners that weapons were legally required to be secured and unloaded when being transported in cars and it was an offence under the Arms Act to discharge a firearm in a public place, such as a roadside.
Prosecution could attract a fine of up to $3000, or a prison sentence, he said.
