The 'grammar vigilante' has been correcting street signs and shop fronts for 13 years. BBC Bristol, home to the elusive graffiti artist Banksy, has a new hooded culprit roaming the streets at night — and his sights are set on bad grammar.

According to the BBC, the man calls himself a "grammar vigilante," and has been correcting the city's street signs and shop fronts for 13 years.

He works in the middle of the night, using stickers to add apostrophes or change bad grammar.

He has even invented an "apostrophiser," a device that helps him add apostrophes in hard to reach places.

He's a "highly qualified professional" by day, according to the Metro, who added that "only a handful of his friends and family know what he gets up to after dark."

Travelling around in a hood in an effort to remain unseen, he told the BBC: "I have felt extremely nervous. The heart has been thumping."

However, he said he doesn't think what he's doing is a crime.

"I do think it's a cause worth pursuing," he said. "It's more of a crime to have apostrophes wrong in the first place."