I am making a site's authentication system in which the sign up form isn't located at index and it isn't going to be at index. If a user is already signed in and wants to fill sign up form, the script tells him that you're already signed in with the following account. It is ok to do that or not? I've seen Google telling that re-enter your password and email is already filled and also picture and name are also displayed.
Why don't you have the site so that if a user is signed in, they don't see the sign-in section of the site?
Or if it's a menu, logged in users see a menu option called logout, all other users see a menu option called login/sign-up.