You attempt to load your social icons twice, once from inside the anchor and again as a background image from the CSS.
When the img fails to load from the markup, because the path or name is wrong, the alt shows. The image also shows because it's loaded again as a background.
Remove that background image and check your img src= path and name.
Correct path to one of your images - http://catalyst.backstageweb.net/wp-...tonTwitter.png