San Francisco has launched an investigation into the installation of a giant "X" sign on the former Twitter headquarters building, which was installed by the building's owner, Elon Musk. The city has stopped workers from removing the iconic bird and logo from the side of the building due to safety concerns, and is now investigating the installation of the "X" sign to ensure consistency with the historic nature of the building and safety of any additions. The outcome of the investigation is yet to be determined.