Contrary to a lot of internet confusion, no leaflets warning about the atomic bomb were dropped on Japanese cities prior to the bombing of Nagasaki. Certainly none indicated any actual possible targets. You can read the whole story here, as well as read the official report on the leaflet operation which is linked to there. The long and short of it is that because of difficulties in producing the leaflets, and a desire to change them to reflect the Soviet entrance to the war, they were not dropped until after the Nagasaki attack. Nagasaki, in fact, got leaflets dropped on it a day after it had been bombed, because the leaflet campaign was not at all coordinated with the bombing plans. There is no way anyone in Nagasaki would have known it was a potential atomic bomb target (and in any case, it was the fall-back target — Kokura was the actual city that was planned to be bombed, originally).