From January 18 to February 14, four large billboards are going up around Seattle that proclaim “Nuclear Weapons Are Now Illegal. Get them out of Puget Sound!” What can this possibly mean? Nuclear weapons may be unpleasant, but what is illegal about them, and how can they be in Puget Sound? Since 1970, under the Nuclear Nonproliferation Treaty, most nations have been forbidden to acquire nuclear weapons, and those already possessing them — or at least those party to the treaty, such as the United States — have been obliged to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.”