As you can see from the screenshot above, that is what your users will see when you enable the Offline mode that offers. As you may already know, this option is used to temporarely block access to your users, and only Administrators can get access by login first.

To enable this option, login to your Joomla Administrator (as Superuser) and under the "System - Global Configration - Site" enable "Site Offline" option. To display your logo enter your logo image into the "Offline image" option.