On a trip to Ford’s Theater, site of President Lincoln’s assassination, Obama paid tribute to the 16th president’s ability to recall passages of Shakespeare’s Hamlet and Macbeth. And with that reference, he unwittingly ventured into what many theater hands believe to be dangerous territory: any mention of the name of the doomed Scottish king in a theater outside of a performance is considered verboten by many actors, who believe it will result in a cursed production — including a greater possibility of injury, bankruptcy, even death.