Icon Class for links

Hi, I need an icon for links. I’d like to have a special link, where I can add as an special attribute. Now I want to make a link-icon before the hyperlink itself. Where is the library and how can I add this icon to it?

My html formatting code ist like this:

{has_att_link}
<div class="em-item-meta-line em-item-taxonomy em-event-categories">
<span class="em-icon-link em-icon"></span>
   <div>
      <a href="#_ATT{link}" target="_blank">external link</a>
   </div>
</div>
{/has_att_link}