Hong Kong SGD25aw 1976-78 10c chalky wmk INVERTED block 4 U/M

Postage Due. 1976-78 10c bright reddish violet wmk Multiple Crown CA diagonal chalk-surfaced paper variety WMK INVERTED upper marginal block of 4 unmounted o.g Scarce. Listed but unpriced in the 2015 Hong Kong sectional catalogue. Originally purchased from Stanley Gibbons (still on their card)