In what appears to have been a half-baked plan, three bags brimming with cannabis have been dumped on the side of a road on the NSW south coast with a sign advertising "free dope".

Shoalhaven police posted pictures of the garbage bags and the sign, which said "Free Dope. Smoke. Mull up" accompanied by a drawing of a cannabis leaf, on their Facebook page yesterday.

Dopey idea ... one of the bags of cannabis.

A local had reported seeing the bags on Bolong Road, Bomaderry, on Saturday morning.

Officers inspected the bags and found 16 kilograms of cannabis leaf inside, police said.