"U.S. citizens should exercise vigilance when in public places or using transportation. Be aware of immediate surroundings and avoid large crowds or crowed places. Exercise particular caution during the holiday season and at holiday festivals or events. U.S. citizens should monitor media and local information sources and factor updated information into personal travel plans and activities."
But really though, isn't this just common sense travel knowledge? Be aware of your surroundings, especially when you are in a packed area and you cannot observe things as easily?