SAN FRANCISCO (KGO) -- The Department of Homeland Security is beefing up its presence at airports, train stations and other travel hubs in the United States in the wake of global travel warning imposed on all U.S. citizens Local authorities are not going into specifics but the San Francisco Police Department does acknowledge receiving a bulletin by the Federal Bureau of Investigation and DHS. The SFPD says their officers are monitoring various areas of the city and will determine if additional resources are necessary. areas of the city and will determine if additional resources are necessary. They say they have...