You might think the reason a particular individual flies a sign at a particular intersection at any given moment is governed by chance. In fact, flagging is anything but random. It is a profession with its own rules and hierarchies. Ninety flaggers, each earning $35 a day, pencils out to more than $1 million a year. Chickenfeed by your standards, maybe, but it’s enough money to spawn careers, cartels, competition, and enforcers.