To add a favicon to your board (works with all styles)

Open: styles > (YOUR STYLE) > template > overall_header.html
Find:
HTML:
</head>
Add Before:
HTML:
<linkrel="shortcut icon"href="http://www.yoursite.com/yourdir/favicon.ico"/>

Change the name of yoursite to your site's URL and change yourdir to the name of the folder where config.php is.

Your favicon should be uploaded to your forum's root (Where your config.php file is) and saved with the name favicon.ico. There are sites to help you build a favicon, such as: Favicon.cc To convert an image to a favicon.ico file use the Favicon Generator

Source : Knowledge Base - Adding a favicon