Stacking Icons
Font Awesome has included CSS to stack icons, allowing you to combine them. In order to do this, instead of inserting the Font Awesome CSS into a Label element's Class attribute, write the full HTML code into its Caption attribute and set its Format attribute to HTML.

An example is shown above. We've used a Label element and set its Caption attribute value to:
<span class="fa-stack fa-lg">
<i class="fa fa-square-o fa-stack-2x"></i>
<i class="fa fa-bars fa-stack-1x"></i>
</span>
The fa-stack class is an FA class that stacks icons. In this example, we've stacked a "bars" icon on top of a "square" icon. Note that we used <i></i> tags, without any actual text, for convenience only; you can also use other tags.

And the resulting icon is shown above.