A self-declared “grammar vigilante” is spending his nights prowling the streets of Bristol and correcting the punctuation on business signs.

Among the mystery man's targets have been signs reading “Vicenzo and Son Gentlemens Hairstylists”, “Herberts the Bakery” and a greengrocer display advertising “potato’s”.

The vigilante, who goes out late at night wearing a black coat and hat, has been correcting the city's erroneous punctuation for more than 10 years.

“The first one I did was way back in 2003,” he told the BBC. “There was a council sign that said ‘Open Monday’s to Friday’s’ and it had these ridiculous apostrophes. I was able to scratch them off.

“Then there was this really gross sign in Gloucester Road: ‘Amy’s Nail’s’. It was just so loud and in-your-face I just couldn’t abide it, so I had to go and apply my wares to this apostrophe. It grates – I think, how can they?”

“I’m a vigilante, I’m a grammar vigilante.”

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The man said he had made an eight-foot-long tool he calls an “apostrophiser”.

This allows him to stick punctuation marks on to high-up displays. He also uses a specially-made stepladder that enables him to work without leaning against shop windows.

By day, he said he works in engineering and spends time with his family.

One recent outing saw him remove an apostrophe from a garage sign reading “Cambridge Motor’s”. The owner told the BBC he was grateful for the vigilante’s work.

“I thank him for what he’s done,” he said. “I don’t mind at all. It’s good to see people still caring about English grammar.”

The grammar vigilante, who uses stickers rather than paint to make his changes, says his “heart is pounding” during his work but denied his alterations amounted to criminal damage.