Why did union soldiers pin their names and addresses to their uniforms?

Han put the last box into the back of his car and turned to look up at his dorm room. he saw himself through the window, laughing with his roommates and sharing his hopes and dreams. he saw all of the hours spent studying and the celebrations at the end of each semester. he smiled fondly as he turned away, got into his car, and drove off. which literary element does the passage contain?