PHILADELPHIA (Reuters) - A civil rights watchdog agency opened an investigation on Monday into a Philadelphia cheese steak restaurant that posted a sign saying "This is America - when ordering, speak English." The Philadelphia Commission on Human Relations complaint effectively opens a case against Geno's Steaks of South Philadelphia, said Rachel Lawton, acting executive director of the agency. The Philadelphia controversy has fed a national debate over immigration in which the U.S. Senate passed a bill that would declare English the national language and politicians have raised objections to a Spanish version of the national anthem.