Six cones appeared on the top of the arches at the weekend.
Senior Constable Tom Taylor, of Balclutha, was unaware the cones had been placed on the bridge and said police would look into the matter.
‘‘It's a bit better than pushing down road signs like they usually do,'' Snr Const Taylor said.
It was likely Fulton Hogan or South Roads would have to retrieve the inappropriately placed cones, he said.