SPECIAL REGULATIONS FOR THE EVALUATION OF MAXIMAPHILY EXHIBITS AT F.I.P. EXHIBITIONS (SREV) 3.1. The postage stamp It must be valid for postage and affixed only on the view side of the picture postcard. Postage-due stamps, pre-cancels, revenue stamps, stamps violating the "UPU (Universal Postal Union) philatelic code of ethics", are not allowed, nor are official stamps 這就是我比較有疑問的地方~~有請前輩說明了