The correct answer is A) AA AA. The International Code signal for calling an unknown station using flashing light is "AA AA". This is the standard signal used to call a station whose identity is unknown, as per the International Telecommunications Union (ITU) Radio Regulations. The "AA AA" signal is transmitted repeatedly to alert the unknown station and initiate contact. The other options are incorrect: B) "UNK" is not an established International Code signal, C) "STA" is the signal for a shore station, and D) "CQ" is the signal used to call any station in a general call, not specifically an unknown station.