MLA

Mills, John, and artist. "Help!" [Graphic]. The Atlantis Press, Boston, 0AD. https://collections.library.yale.edu/catalog/16047629.

APA, 6th edition

Mills, J., & artist. (0 C.E.). "Help!" [graphic] [War posters, Posters, Lithographs]. The Atlantis Press, Boston. https://collections.library.yale.edu/catalog/16047629.