"When it just had the eye missing it looked a little bit creepy. I certainly don't condone [vandalising signs] but when you're in politics it does happen from time to time and you roll with it. Sometimes it's good to make light of it."
This week, election opponents National and the Conservatives acknowledged they had begun using motion sensor cameras to catch any would-be sign vandals, though Labour and other parties had not taken the same step.
The work with the marker pen was done "a couple of weeks ago", Ms Ardern said, although someone had since been back and removed some of her teeth.
"We've kept it [the pirate sign] there. I just hope nothing further happens to it. If it gets too ratty, we'd have to take it down."
Some of Ms Ardern's signs had had parts of her face removed, as if someone were trying to create a bizarre "potato head or a ransom note".
A police spokesman said the most likely charge that could be laid against vandalism would be wilful damage, although that would probably not apply to the owner of a sign.