When bad punctuation strikes storefront signage in Bristol, England, a self-styled apostrophe avenger springs into action. The BBC reports that an unidentified man has spent years venturing out at night to correct infractions against the English language spotted in public street and retail signs.

Although the man holds grudges against all forms of errant punctuation, he spends most of his time addressing wayward apostrophes using a tool he built himself. Dubbed the “apostrophiser,” it can either add or subtract apostrophes from signs, depending on the correction needed, using adhesive tape. He also carries a ladder.

Often referred to as "the Banksy of punctuation," this human version of Wite-Out says he was lured into a life of mildly invasive graffiti when he decided to scratch out a misplaced apostrophe on a whim in 2003. “It was a council sign—Mondays to Fridays—and had these ridiculous apostrophes,” he said. “I was able to scratch those off.”

Jon Kay via Twitter

While some businesses appreciate the unsolicited correction, others consider the forced changes rude. A shop called Tux & Tails previously identified itself as a “Gentlemans Outfitters” before the rogue corrected it to “Gentleman’s Outfitters.” Owner Jason Singh says the defacing of the sign could cost him thousands of dollars to fix because the paint the man used isn’t meshing well with the vinyl surface. Singh promises to bill the vigilante for the damage if he ever learns his identity.

The BBC did not reveal the man’s name, nor did they appear to hand over any information to authorities. Despite the sketchy legal nature of his work, the vigilante said it was “more of a crime” to leave the incorrect punctuation standing. A half-hour BBC Radio 4 documentary on his work aired on Monday.

The Bristol vigilante isn’t the first of his kind: Two anonymous artists in Quito, Ecuador, have been correcting that city’s graffiti for years, using red spray paint to point out spelling and grammar mistakes. Known as Acción Ortográfica Quito (Quito Orthographic Action), they’ve inspired a rash of imitators worldwide. All of which is good reason to hire a copyeditor before you write in public.

[h/t BBC]