When someone is banned from these forums it will tell you that the user has been banned right? So what's this ( unregistered or deleted user ) mean? Can you delete your account?
You can request an account deletion by clicking on your name at the top of the page / My Settings / Profile Settings / Delete Account. When your account is deleted, none of your content will be searchable in the database, but it will remain viewable. Your username will say guest_ codswallop after deletion.
When looking at the user's posts it looks like this. When clicking on the username "Deleted Member" It takes me to a page that reads "We could not find the member whose profile you were attempting to view."
You're using the mobile app? The interface and the layout is different than on a PC/Mac. Here is what a deleted account looks like on a PC. What exactly are you wanting to know? Are you trying to find a deleted member? Once deleted, you will get that message you posted up above.
No I'm using the forum on a pc. I'm only asking because I noticed a member seemingly disappear all of a sudden. I was curious when I went back through private messages and clicked on the message from that user that's what I found.