What you say when you see one of the most heinous crimes against the english language known to man. It's when an apostrophe is put in a plural noun (WHERE IT DOESN'T BELONG!), therefore indicating that the noun somehow owns something...
sign: BOOK'S FOR SALE!
my smart friend: SHEILD YOUR EYES! APOSTROPHE CRIME!
me: *smacks forehead* So... that book owns a for sale? That's interesting... MY GOD PEOPLE WHEN WILL YOU LEARN!?!?