An Act New Zealand sign in Maheno was vandalised with black marker last week, turning party leader David Seymour into Adolf Hitler.
The sign was taken down and replaced at the weekend, but it was vandalised again, this time turning Mr Seymour into a member of the Ku Klux Klan.
The white hood was made with a piece of white cloth on a triangular wooden frame, which was screwed on to the sign.
Eye holes were burnt out, making it look more like a KKK hood.
Act candidate Sean Beamish said it was an "admirable effort", but every time a sign was damaged he had to replace it during his own time.
There was always a mixture of politically motivated vandals and those who just did it for fun, but how the signs were vandalised generally indicated which of those was responsible, he said.
An Act spokesman said vandalism of political signs was "childish behaviour".
The party had plenty of signs in reserve and seeing the damage just made "volunteers more determined to get our signs out there".
National Party signs were cut up and left damaged around Oamaru last week.
National candidate Miles Anderson said all parties suffered from vandals.
It was frustrating as it cost "quite a bit" to replace them.
Labour candidate Ethan Reille said there had not been many issues with his campaign so far.
Vandalism happened to all parties all over the country, he said.
It was up to candidates to try to reach the sort of people who vandalised the signs.
