Van Halen did dozens of shows every year, and at each venue, the band would show up with nine 18-wheelers full of gear. Because of the technical complexity, the band's standard contract with venues was thick and convoluted -- Roth, in his inimitable way, said in his autobiography that it read "like a version of the Chinese Yellow Pages." A typical "article" in the contract might say, "There will be 15 amperage voltage sockets at 20-foot spaces, evenly, providing 19 amperes."
Van Halen buried a special clause in the middle of the contract. It was called Article 126. It read, "There will be no brown M&Ms in the backstage area, upon pain of forfeiture of the show, with full compensation." So when Roth would arrive at a new venue, he'd walk backstage and glance at the M&M bowl. If he saw a brown M&M, he'd demand a line check of the entire production. "Guaranteed you're going to arrive at a technical error," he wrote. "They didn't read the contract.... Sometimes it would threaten to just destroy the whole show."
In other words, Roth was no diva. He was an operations expert. He couldn't spend hours every night checking the amperage of each socket. He needed a way to assess quickly whether the stagehands at each venue were paying attention -- whether they had read every word of the contract and taken it seriously. In Roth's world, a brown M&M was the canary in the coal mine.