Signs supporting controversial senator Fraser Anning were attached to the pole in the middle of Canberra's rainbow roundabout on Wednesday morning, but were taken down less than two hours later.
Fraser Anning's Conservative National Party is running in the Senate race in the ACT, but Mr Anning himself is running in Queensland.
The signs were attached to the pole in the middle of the roundabout of Lonsdale and Elouera Streets in Braddon. The roundabout was painted in rainbow colours and decorated with rainbow lights to celebrate same-sex marriage being made legal in Australia.
Mr Anning voted against same-sex marriage in 2017 and has said he is committed to repealing the laws that allowed people to marry someone of the same gender.
According to the ACT government's electoral advertising guidelines, signs must not be placed at roundabouts.
A witness saw two men arrive in a white van and wearing hoodies about 11.30am Wednesday and put the signs up using a ladder.
By 1pm, a Canberra Times photographer saw two other men arrive and remove the signs.
They identified themselves as locals who heard about the signs on social media and had decided to remove them on their own.
ACT Policing arrived in the area at the same time and spoke to the men who removed the signs.
The lead Senate candidate for Fraser Anning's National Conservative Party, Shane Van Duren, said he had asked volunteers to put the signs up and hadn't specified particular locations.
He maintained that he had complied with Australian Electoral Commission rules and wasn't aware of ACT rules.
Mr Van Duren said he believed in "traditional marriage" and didn't see why people would be offended if Mr Anning's signs were on the landmark.
Minister for City Services Chris Steel confirmed he had received a complaint about the signs and an investigation would happen.
"These signs appear to have been placed illegally and I have asked TCCS to investigate and act accordingly," he said.