The Killers

One morning, hit men Charlie (Lee Marvin) and Lee (Clu Gulager) enter a school for the blind and terrorize the principal until she reveals the whereabouts of a teacher, Johnny North (John Cassavetes). As the hitmen walk toward North's upstairs classroom, the teacher receives a call warning him of their arrival. Johnny sadly responds, "It's okay. I know them." As he calmly waits at his desk, Charlie and Lee enter and shoot him multiple times.
As they depart by train, Charlie is bothered that North refused to flee, and that they were paid an unusually high fee for such a simple hit. He and Lee run through what they know about the man they have just killed. Johnny was once a champion race car driver whose career ended in a violent crash. Four years before his death, he was involved in a million-dollar robbery of a mail truck. Tempted by the missing million, Charlie and Lee visit Miami to interview Johnny's former mechanic.
Earl Sylvester (Claude Akins), who considers himself Johnny's only friend, is devastated to learn of his death. In between sobs and gulps of whiskey, he tells the story as he remembers it. Johnny North was at the top of his profession when he met the beautiful Sheila Farr (Angie Dickinson). Johnny fell in love and planned to propose marriage after winning his next big race. However, Johnny's late nights with Sheila had left him disoriented from lack of sleep. His racing career ended with a fiery crash.
At the hospital, Earl revealed to Johnny that Sheila was the mistress of mob boss Jack Browning (Ronald Reagan). Known for her extravagant taste, Sheila has already cheated on Browning with several other sports figures, all of whom met bad ends. Enraged and heartbroken, Johnny rebuffed Sheila's attempts to explain and cut his ties to her.
Intrigued, Charlie and Lee approach a former member of Browning's crew, who also reveals his memories. After the crash, Sheila found Johnny working as a pit mechanic. She says a much better job might soon be his for the taking. Browning was planning the robbery of a U.S. postal truck. On Sheila's recommendation, he agreed to Johnny as his getaway driver.
Although Johnny still felt betrayed, Sheila said that she had always regretted losing him. Johnny forgave her. He also helped Browning by souping up the getaway car. Browning, however, was enraged when he learned that Sheila had returned to Johnny. In a deliberate provocation, Browning brutally slapped Sheila in front of Johnny, after she defied him. Johnny punched Browning and threatened to kill him if he ever hurt Sheila again. They agreed to "settle this" after the robbery.
Browning and North placed a phony detour sign to send the mail truck onto an isolated mountain road. When the truck stopped, the gang held it up at gunpoint, loading more than $1 million into the getaway car. Johnny then forced Browning out of the moving car, driving off alone with the money.
After listening to this story, Charlie and Lee pay a visit to Browning, who is now a real estate developer in Los Angeles. Browning insists he is now an honest businessman and has no idea what happened to the money. He reveals that Sheila is staying at a hotel and arranges a meeting with her.
To deprive Browning of time to plan an ambush, Charlie and Lee call at Sheila's hotel several hours earlier than agreed. At first Sheila denies all knowledge of Johnny or the money. Charlie and Lee beat her and dangle her by the ankles out a seventh-story window. Terrified, she tells them the truth.
The night before the robbery, she told Johnny his life was in danger. Browning, she said, was planning to kill him and pocket his share. Johnny wanted to kill Browning on the spot. Sheila insisted she had a better idea. On her advice, Johnny threw Browning out of the car and drove the money to Sheila.
As the two lovers met in a hotel room, Browning showed up. Sheila asked Browning to "do it quickly," and the gangster shot Johnny, severely wounding but not killing him before Johnny escaped. It turned out Sheila and Browning were husband and wife. Sheila expressed fear that Johnny would seek revenge, so Browning hired Charlie and Lee to murder him.
Charlie now understands at last why Johnny refused to flee. The only man who refuses to run is a man who considers himself to be already dead. Sheila's betrayal had already killed Johnny long before the bullets ever touched him.
Charlie and Lee, with Sheila in tow, intend to confront Browning, but he is waiting nearby with a sniper rifle. He kills Lee and wounds Charlie.
Browning and Sheila return home, where they prepare to flee with the money. A mortally wounded Charlie makes it there in time. Sheila, at last revealing her sociopathic nature, frantically denies any role in Johnny's death, insisting that her husband alone was responsible. Charlie calmly shoots Browning dead. He turns his revolver toward Sheila. When she again pleads for her life, Charlie snarls, "Lady, I don't have the time!" He kills Sheila with a single bullet and staggers out the door. Charlie falls dead on the lawn while still gripping the money, as a police car in the background makes its way towards the house.

Question: A phony detour sign was placed to send what onto an isolated road?
Answer: the mail truck