Meet the 'Grammar Vigilante' of Bristol
3 April 2017 Last updated at 00:29 BST
For years, it has been rumoured that somebody has been going out late at night, correcting bad punctuation on Bristol shop fronts.
The self-proclaimed "grammar vigilante" goes out undercover in the dead of night correcting street signs and shop fronts where the apostrophes are in the wrong place.
Jon Kay meets grammar's answer to Banksy and reveals the extent of his one man mission to improve standards.
Listen to more in The 'Apostrophiser', Radio 4, 20:00 BST, Monday 3 April, or afterwards on the BBC iPlayer.