New York City Mayor Bill de Blasio will not be marching in the nation’s largest St. Patrick’s Day parade, deciding to skip one of his city’s signature celebrations because the event organizers refuse to let participants carry pro-gay signs.De Blasio will become the first mayor in decades to sit out the traditional march along Fifth Avenue. “I will be participating in a number of other events to honor the Irish heritage of this city,” said de Blasio on Tuesday during an unrelated press conference at City Hall. “But I simply disagree with the organizers of that parade.” …