fa-icon-external-link.css

/* Mark external links that have the rel="external"
   attribute set with a FontAwesome icon. */

a[rel~="external"]:after {
    content: "\f08e";
    display: inline-block;
    font-family: FontAwesome;
    font-size: 80%;
    font-style: normal;
    font-weight: normal;
    padding-left: 3px;
    text-decoration: none;
}