Lieutenant Jeremy Foster is the only soldier escorting Claire and Dougal to the British camp who does not wear a wig. As an officer, a wig would have been a part of his military uniform.
When Jamie makes the sign of the cross (blessing or crossing oneself), he has used both the Western Christian sequence as well as the Byzantine sequence. For Roman Catholics, it was usual to make the sign of the cross as Western Christians: forehead, chest, left shoulder then right shoulder.