On September 3, 1968, the US Civil Administration sent a letter in the name of Civil Administrator Stanley S. Carpenter to Matsuoka Seiho, chief executive of the Government of the Ryukyu Islands. The letter proposed installing signboards to prevent illegal entry into this area in the future, warning that a system for checking the area was in place, that the area would be patrolled by the Ryukyu Islands government police, and that not having an entry permit made entrants liable to prosecution and fines under the laws of the Ryukyu Civil Administration. The US military informed Matsuoka that they had made preparations for performing occasional military flights over the Senkaku group. (Ref. 1)
Ref.1 ："Keikokuban secchi teian shokan" (Letter regarding Installation of Warning Signboards), from Office of the Civil Administrator, the Ryukyu Islands US Civil Administration, Department of the Army (September 3, 1968). Copy in OPRF Center for Island Studies.