[Nuvola]

At the top under the navigation links at the top (Home, Forums, Shops, etc..) There should be a few links right under that which say your username, Logout, Settings, and Achievements. Click 'Settings' and to the left under 'Your Control Panel' should be a 'Settings and Options' section, and the second link down says 'edit signature' 8D Lemme know if you find it!