Designed by an artist working on the Illinois WPA Art Project in the late 1930s, this bold-red question mark drew the public's attention to the threat of smallpox. Promoting childhood vaccinations became an important strategy toward preventing outbreaks. The prevalence of the disease in the United States diminished in the twentieth century, and the World Health Organization delcared in 1979 that it had been completely eliminated.

Artist: Unknown
Source: Library of Congress