The “You buy a liberty bond–Lest I Perish” poster was used during World War 1 to encourage the purchase of war bonds (known at the time as liberty bonds) to help fund the U.S. war effort.

A Liberty Bond was a war bond  sold in the United States to support the allied cause in World War I. Subscribing to the bonds became a symbol of patriotic duty in the United States and introduced the idea of financial securities to many citizens for the first time.