Why are there crosses on all windows during world war 2?

During World War II, crosses were often painted on Windows as a means of identifying buildings that were used for specific purposes, such as hospitals or schools, to protect them from bombing raids. These markings were intended to signal to pilots and military personnel that these structures were not legitimate military targets, thereby minimizing civilian casualties. Additionally, the crosses served as a form of visual communication to aid in the organization and logistics of wartime efforts.