SAVANNAH, Ga. — Protesters seeking to carry signs in an area being secured for Vice President Mike Pence to participate in the South’s largest St. Patrick’s Day parade won a brisk free speech fight Friday as city officials in Savannah backed off prohibiting signs and posters at the event. City officials reversed course and announced signs would be allowed immediately after the American Civil Liberties Union filed a federal lawsuit Friday morning against City Hall, saying a blanket sign ban during Pence’s visit Saturday would violate the speech rights of parade goers. “It’s a great day for the First Amendment,” said Will Claiborne, a Savannah attorney who joined the ACLU in filing the suit.