Board Thread:Questions and Answers/@comment-34660304-20160530142632/@comment-27542229-20160530203701

Second revision - In the cases when the show has not displayed a house's coat of arms, we normally use the current shield for both left and right shields. This is really common with members of the Night's Watch. A lot of these characters come from noble houses but their house's coat of arms have never been shown.

Or, we use the great house's shield when a lesser house's shield is not available. For example, Alliser Thorne comes from House Thorne, which has no shield in the TV show, but House Thorne was a House Targaryen loyalist during Robert's Rebellion. So we use House Targaryen on the left to denote his previous allegiance with the Night's Watch on the right to denote his current allegiance.