The answer is a Stamp.
First class stamps are valued at 45 cents as of 2012. You may not know that stamps must always contain three important pieces of information in their design: subject, stamp value, and country of origin.
Of interest, the 2013-14 "duck stamp" just went on sale June 29, 2013 (it's the 80th in the series). The stamp is also known as the "Migratory Bird Hunting and Conservation" stamp. 98 cents of every dollar spent goes to the purchase of wetlands. Find more info here.