This claim is false. A photo of the sign was placed and posted by the WowserNation. They describe themselves as an art collective that are "exploring the Australian nanny state through subversive street art." WowserNation placed many fake government signs throughout Sydney, Australia. The post that was made of the sign shocked many who weren't aware of the joke. Facebook flagged the post as false information. Many people took the sign seriously, spreading misinformation and ridicule about the public street art.
Source: In Australia, "All joggers must wear a helmet.”