"If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)"

GNU General Public License, version 2
Section 2c

The world of GPL'ed web applications often cites this passage of the GPL as a legal requirement to display that application's copyright notice at the bottom of each page. We do not believe that this requirement is legally enforceable under the GPL. Is Enano, or any other CMS for that matter, a program that is started at a terminal, and you type commands to make it do certain things? No. Therefore, is Enano, in a legal sense, an interactive program? No. You are not legally required to preserve Enano's "About Enano" page or the link at the bottom of generated pages.

However...

Enano is still a relatively new addition to the huge world of content management systems. If you like Enano, the least you can do is to help spread the word. So while we will never under any circumstances pursue any sort of legal action or GPL violation if you remove the "Powered by Enano" text, it doesn't help spread the word at all, and it means that Enano will get less public attention. This notice is three words long and it sits right next to your copyright notice. So it's not like it occupies three full lines like the notice in PHP-Nuke does. The word Enano links to a nice little page that explains the licensing terms and provides a copy of the GPL. It doesn't look horrible, and it doesn't get in anyone's way. For this reason, we are asking people to please be considerate enough to link back to Enano's about page - it's really the least you can do. If you refuse to include this link, we may ignore your requests for help, or otherwise respond in a terse way when you ask for support. Linking back is considered a way of saying "thank you" to us for giving you your website's personality.