Millions have come to love Daniel Rodriguez as the so-called “singing policeman,” the New York City cop who helped bring the country an uplifting spirit of promise and hope with his stirring rendition of “God Bless America” after the Sept. 11 terrorist attacks. Since then, he has studied under Placido Domingo, retired from the police force and released three albums: “The Spirit of America,” “From My Heart” and “In the Presence.”