NEW YORK (AP) — Authorities are trying to identify the source of what appears to be a mock movie poster warning that al-Qaida wants to come back to New York City.The New York Police Department and the FBI discovered the graphic on the Internet on Monday. It features a photo of the city at sunset with "Al Qaeda" in bold type followed by "Coming Soon Again in New York."Both the FBI and the NYPD said investigators have found no evidence so far that the posting represents a credible threat against New Yorkers.