Quote from : Men at Arms Book

You see," said Colon, "thieves are here. I mean, it's . They're a certain amount of thieving. Not that they do much these days, mind you. If you pay them a little premium every year they give you a card and leave you alone. Saves time and effort all around." "And all thieves are members?" said Angua. "Oh, ," said Carrot. "Can't go thieving in Ankh-Morpork without a Guild permit. Not unless you've got a special talent." "Why? What happens? What talent?" she said. "Well, being able to survive being hung upside down from one of the gates with your ears nailed to your knees," said Carrot.