Click on manage site, settings, manage settings. On that place is where you enter your community's title. Make sure you have one there, otherwise, one won't be in the login box. Once you've put one there, if indeed that is the problem, it may take a little while to see it take effect for logged out people/visitors, including yourself. If that happens in this case, or any other case in the future, you can speed the process up by clicking on manage site, settings, manage settings, advanced options, and then disabling the page cache for on hour by clicking the little link.
