Apply favorites icon per portalThe small icon that is shown in your browser url bar, and also used when a user bookmarks a page is known as the favicon. By default browsers will look for a file named favicon.ico in the root of a website and use it.
DotNetNuke providers additional support for this as well, allowing portal specific favicon's. To use this place (or replace) your “favicon.ico” in the portal root folder. For example in “..\Portals\0” or “..\Portals\1”, etc.
Note: with the 6.0 release DotNetNuke added an the ability to set this under admin->site settings.