Tagging is the act of writing your name or your own sign on walls, trains, bridges and other public places without being allowed to. The name you write is a tag: short, quick, always the same, so people recognise it. Tagging is done fast — often in seconds, often at night — because the person doing it does not want to be caught. Notice the difference between tagging and the wider word graffiti. Graffiti is the whole family, from one rude word scratched on a desk to a whole wall painted like a picture. Tagging is one narrow member of that family: writing a signature, over and over. Painting a large, careful, coloured picture on a wall is usually called doing a piece or painting a mural instead. Because tagging is against the law, the word usually appears in unhappy sentences — city councils complaining about it, shop owners cleaning it off, police reports. It is a normal noun and you can use it comfortably in writing. Grammar note: tagging is the -ing form of the verb tag, so it works both as an action noun ("Tagging is a problem here") and inside a verb phrase ("He was tagging a wall"). And be ready for the completely separate everyday sense — tagging a friend in a photo online, tagging files, tagging clothes with prices. Same word, no crime involved.