Let us answer it with W.S.S. : war savings stamps issued by the United States Government.

Bibliographic Details
Corporate Author: United States. War Loan Organization. Savings Division
Format: Photo
Language:English
Subjects:
Description
Item Description:Original artwork for a potential propaganda WW1 poster issued by the United States Government.
The war savings stamp (WSS) was a patriotic program used by the Savings Division, War Loan Organization, U.S. Treasury Department to help fund participation in World War I, and was principally aimed at school-age children. Savings stamps were available in ten cent and twenty-five cent versions, and provided interest. In some cases collections of stamps could be redeemed for war bonds.
Subject: Silhouettes of 2 soldiers faces (representing America and Germany) underneath 2 large yellow question marks.
Physical Description:1 poster : color ; 57 x 78 cm