Postage due is the term used for mail sent with insufficient postage. Manchukuo had its own issued banknotes and postage stamps. Some may provide additional services, such as selling postage stamps. PhotoStamps are sold as a sheet of 20 postage stamps. Women stamp collectors date from the earliest days of postage stamp collecting. Wombats have featured in Australian postage stamps and coins. Two U.S. postage stamps relate to Kearny. Governments have sometimes combined the functions of postage and revenue stamps. Gray was also interested in postage stamps. Her face is on postcards of Berlin and 1989 German postage stamps. This was related to a special commemorative postage stamp issue. John Muir was featured on two U.S. commemorative postage stamps. Engraved renditions of Federal Hall appear twice on U.S. postage stamps. The platypus has frequently appeared in Australian postage stamps and coins. His likeness also appears on many postage stamps.