Is covering the head (with a skullcap, ghutra, turban, or other head covering) a Sunnah?

Covering the head is commendable and a part of complete adornment. It was the custom of the Prophet (peace and blessings be upon him) and his companions. However, it is not an act of worship but rather a custom. Its legal ruling varies according to the customs of each country; it may be considered a blemish to one's honor in one place and not in another. Wearing a turban is not among the emphasized or unemphasized Sunan, as the Prophet (peace and blessings be upon him) wore it in conformity with the custom of people in his time. The general principle is that a person should follow the customs of his country in dress, unless they are forbidden, in order to avoid the prohibited clothing of ostentation.