This Guatemala airmail stamp, originally issued as a Red Cross commemorative (4 centavos), features a bold red cross on a radiant green background and a portrait of Rafael Ayau, noted Guatemalan philanthropist and founder of the country’s first orphanage and charitable institutions. Your example bears the special black overprint “Feria Mundial de New York,” referencing the New York World’s Fair, making it a desirable overprint variety sought after by specialists. Printed by Staatsdruckerei Wien, the stamp combines humanitarian, airmail, and overprint appeal—an excellent piece for collectors of Red Cross issues, Central American philately, and World’s Fair postal history.