This annotation is used to configure the template that is used to render the page title when the controller tagged with this annotation is accessed:

// ...
use Oro\Bundle\NavigationBundle\Annotation\TitleTemplate;

 * @TitleTemplate("The page title")
public function demoAction()
    // ...

You can use arbitrary placeholders here which you then have to replace later on in your template using the oro_title_set() Twig function:

{% oro_title_set({params : {"%username%": fullname }}) %}