I get signed in automatically, I don't like this. Also I do not see any option to logout or signout
I don't know how you can avoid being signed in automatically. An authentication token is set when you first log in and you will be logged in automatically until the token expires. Presumably, you can delete this (perhaps by clearing your cookies) but I don't really know how.
Logging out, however, is easy:
Just click on the Stack Exchange menu in the top bar, and then click on "log out".