Netherlands East Indies. (Singapore). 1941. Advertising Air Mail envelope for the Chevrolet Motor Car (illustration on reverse) headed 'An Hok Liong & Co. Telokbetong (Sumatra), addressed to New York bearing Netherlands Indies SG 408, 35c purple, SG 429, 10c vermilion and SG 440., 1g violet tied by Tand - Jong date stamp '30th Dec 41' with 'Door Censuur Geopend' tied by 'Censuur/ 5' date stamp in red '6th Jan 42' with circular 'Dev/ 10' and 'Ec. C.' censor in carmine and large '0' (meaning unknown), routed via Singapore with 'D' an '26' censor cachets on face.
An illustration of the '0' is illustrated in "Nico de Weijer's' book on the censorship of the Dutch East Indies. Perhaps the stamp was thought not to be valid !