A favicon is a graphic image (icon) associated with a particular Web page and/or Web site. Many recent user agents (such as graphical browsers and newsreaders) display them as a visual reminder of the Web site identity in the address bar or in tabs

To add a favicon to your Web site, you'll need both an image and a method for specifying that the image is to be used as a favicon. This document explains the method preferred by W3C for specifying the favicon. There is another common method that is illustrated below, with an explanation of why that method is inconsistent with some principles of Web architecture

First of all, You should create the icon image, the format for the image must be 16x16 pixels or 32x32 pixels, using either 8-bit or 24-bit colors. The format of the image must be one of PNG (a W3C standard), GIF, or ICO. Once you have the image, please upload this image to  your root directory of your website, ie. http://example.com/myicon.png

Then edit template file page_index.html and member_index.html located in folder themes then paste the following code to your html code  between the <head> and </head> tags. Make sure to replace example.com with your domain name!

<link rel="icon" type="image/png" href="http://example.com/myicon.png">

Save your files page_index.html and member_index.html then visit your site to see the new favicon image in your web browser.