The city of San Francisco has launched an investigation into Twitter headquarters, after a giant “X” was installed on the roof of the building without a permit amid the social media company’s ongoing rebrand. The “X” was installed on top of the building in downtown San Francisco Friday, after police stopped workers earlier this week from dismantling the Twitter sign on the side of the building, according to The Associated Press. They reportedly lacked the proper permits and had not taped off the sidewalk as a safety measure. Two new complaints were filed with the San Francisco Department of Building...