War Savings Stamps (W.S.S.) Thriftettes War Bond Drive c.1918

The United States Treasury Department issued its first war savings stamps in late 1917 in order to help pay for the costs incurred through involvement in World War I. The estimated cost of World War I for the United States was approximately $32 billion, and by the end of the war, the United States government had issued a total of $26.4 billion in debt. Although national campaigns had aimed to sell $2 billion in war savings stamps, they ultimately accounted for about $0.93 billion, or 3.5 percent, of the total debt issued. Despite the low proportion of total debt purchased as war savings stamps, they represented real additional savings whereas other issues were at least partly monetized already. In addition, government and society leaders utilized the war savings stamps program as a vehicle to teach the importance of saving and thrift.

Along with the War Savings Certificate stamps, the Treasury also issued a set of 25-cent Thrift stamps, which bore no interest. The purpose of the Thrift stamps was to allow individuals without the means to purchase a War Savings Certificate stamp outright to gradually accumulate enough Thrift stamps to exchange for one later. The Treasury supplied Thrift cards, to which a total of sixteen Thrift stamps could be affixed. A full Thrift card was worth four dollars and could be combined with the appropriate number of cents to purchase a War Savings Certificate stamp.

https://en.wikipedia.org/wiki/War_savings_stamps_of_the_United_States