"Maybe," Rincewind says slowly, wiping away crumbs, "he wears it so people will think he's a soldier. Then, when someone wants one, they'll think he's busy and not bother him. That's really a very good idea," he says admiringly. "It'd get a little toasty in summer, but what's a bit of discomfort to not having to fight?"
"Ever hear of Ankh-Morpork?" he asks. He'll be able to tell by the reaction. Once you've heard of Ankh, you don't forget. Even if you've never been there.