Thanks, I did see this extension but good to know it can be done with plain css as well. The css posted picks up the users who liked the posts (for example at the bottom of your post when applying css on this page). Below has minor tweak that will restrict to the post header (and also exclude from user card on hover).
article.CommentPost.Post.Post--by-start-user .Post-header h3 span.username:after {
content: "Author";
background: #F05D1D;
border-radius: 4px;
padding-left: 10px;
padding-right: 10px;
color: #fff;
margin-left: 14px;
}
