Some jobs require special clothing or uniforms. Sometimes these special clothes are meant to protect workers or the people they work with. An emergency room doctor, for instance, may wear special clothes to protect herself from blood and infectious agents as well as to protect patients from the germs and impurities that may be present on ordinary clothing. Most often, though, special clothes or uniforms are worn so that workers can be easily recognized by other people. Occupations that require uniforms are frequently service jobs, where workers help or perform services for other people. Workers in stores and restaurants frequently wear uniforms so that customers know whom to ask for help or service. Uniforms help police officers do their jobs better, because people recognize them and go to them for help or give them the cooperation they need to maintain the law. On the battlefield, soldiers wear uniforms to identify which country they are from, signaling whether they are friends or enemies.