Thailand. (India used in Aden - Siam used in Kedah). 1903. Book Post front addressed to Singora, Siam bearing India SG 123, 1a carmine tied by Aden date stamp '2nd Mar 03' with Bangkok transit and routed via the steamer "Coromandel" with 'Penang To Singapore' marine sorter dated 'April 4', Penang transit '7th April' and Siam used in Malaya Kedah '7.4.03.' and forwarded to Singora with arrival date stamp '17th April' on face.
Very rare item paying the Book Post rate from Aden into Kedah and Siam.