Adding Font Awesome icons to tags

I have a cool idea. Tags could add icons http://fontawesome.io/icons/

Should be possible by adding some custom CSS.

anyone know why there are two?
Im Use this:

 .item-tag1 :before {
 content: "\f000";
 font-family: FontAwesome;
 }

.item-tag1 > a > span:before {
    content: "\f000";
    font-family: FontAwesome;
}