Back in the mafia’s heyday, FBI and IRS agents had a set of surveillance rules. If one mobster showed up in town, pay notice. If two arrived, be suspicious. If three or four were in the same vicinity, something was going down. And if five or more headed to the same neck of the woods, a meeting of consiglieri or La Cosa Nostra’s council was likely happening. (This, because there were always five families in New York and some adjunct families elsewhere that made up the council’s leadership.) There also was another rule of thumb: Mobsters would always have the...