This poster urging Americans to buy war bonds was issued in 1918.
This giant “Buy Defense Bonds and Stamps Now!” hung in Grand Central in 1941.
Found this World War I-era propaganda poster at the Smithsonian Institute, which notes,
At the onset of American involvement in World War I, President Woodrow Wilson had to persuade the American public that neutrality could no longer be maintained, and that everyone’s constant support and sacrifice were required to win. To do this, he created a task force that produced over 25 million copies of 2,500 different posters. The United States produced more propaganda posters than all other countries involved in the war combined, even though it was only engaged in the war for 20 months.