Apple's £1

A greengrocer's sign, seen in a window: Apple's £1.

One apple. One pound. And one apostrophe doing a job nobody asked it to.

That little mark means belonging (the apple's core) or a squished-together is/has (the apple's gone off). What it does not mean is more than one apple. Plurals go bare: Apples £1. No apostrophe. None. Not even a small one for luck.

It's the most common punctuation slip in the English-speaking world, and honestly? The apple doesn't mind. But now you'll see it everywhere. Sorry.

The apostrophe, in full — Pillar 6, punctuation.