The title "Arrow on the Doorpost" comes from the practice of many native American tribes of sticking a tomahawk or arrow into a tree or gatepost marking the the outer boundary of their land during times of war with other tribes. The tomahawk or arrow would be planted at the beginning of the conflict and not removed until the conflict was resolved. In some modern native American families this tradition has been updated, and the family will similarly mark a post on a verandah or tree in the front yard while a family member in service to the military is deployed in combat.
The episode was originally titled "Pale Horse". TV critic Kevin Skinner said, speaking of the episode name, that he didn't get it and wishes show-runner Glen Mazzara had stuck with 'Pale Horse' and kept the original scene with Daryl finding a headless rider on a living horse which tied into the episode title.
Daryl has a new crossbow in this episode
The Governors surname is revealed as 'Blake'.