Underlining the significance of the deal, President Juan Manuel Santos and the top commander of the Revolutionary Armed Forces of Colombia, or FARC, a rebel fighter known by the alias Timochenko, signed the accord in the colonial city of Cartagena. In a ceremony charged with symbolism befitting a historic moment that generations of Colombians thought they would never see, the more than 2,500 guests were asked to wear white as a sign of peace and Santos signed the 297-page accord with a pen made from a recycled shell used in combat. Earlier Monday, Santos and the foreign dignitaries attended a Mass celebrated by Cardinal Pietro Parolin, the Vatican’s secretary of state, at a baroque church named for St.