Sayyiduna Abu Umamah (may Allah be pleased with him) said: "Whenever the Messenger of Allah (peace and blessings be upon him) appointed a governor, he would always tie a turban on him, and let one end of it hang down from the right side towards the ear."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7610