CHINA. 1918 registered "On Service" cover from Peking (2 May 1918 cds) to Wenchow (9 May arrival c.d.s.) via Shanghai with May 5 c.d.s. "POSTAGE PAID" and registration chops also on front. "On Service" mail should be always free of postage, thus exceptionally unusual with postage paid chop. Should not be of private usage requiring postage as there is numbering written in the lower left corner. RARE. (Photo). Est. 400 - 500 CHF.