In the case of a Guest, my understanding is, you have limited features available for them when compared to a Registered User who has signed in.
The following is assuming your application heavily depends on a Login, which in the case of an RSS Reader, need not be necessary.
In order to let someone know, they're not yet signed in/registered, the best way I think to do this is slide the Navigation Drawer out right at the launch of the application to showcase the limited features and a Sign In/Register option in the Drawer, which in the header will be labeled as Guest with the blank profile picture.
Ink the other options gray, if they cannot be accessed by the guest.
Keep the options clickable and if the user has not logged in, launch the activity the option intents to and showcase a Fragment to Login, suggesting the feature cannot be accessed by a Guest account and you can log in below. 9GAG App does this very well with NSFW posts.
Once logged in, you only need to make the options available if originally you did not.