How about making something so that it warns us before posting that we are not signed in or something? Or that you can only posted if signed in. Several times already I have accidentally posted under a Guest name because I forgot to sign in. Also, allowing guests to post whitout some sort of name verifying or without requiring them to register will encourage people to make comments they wouldn't make otherwise due to their identity being known.

I believe the only way round members posting as a guest is to ensure that when you login that you check the box asking 'remember me'.
Other than that, one has to try to remember to look at the top of the page and check your login status.

Regarding the other issue, it seems that if one doesnt register then they will automatically post as an anonymous guest.
I have noticed that sometimes there are posts that mention name and have 'Guest' underneath with no other details like post count, etc.
I have no idea how or why this happens so if anybody else knows please let me know!