A guestbook (also guest book, visitor log, visitors' book, visitors' album) is a paper or electronic means for a visitor to acknowledge a visit to a site, physical or web-based, and leave details such as their name, postal or electronic address, and any comments. Such paper-based ledgers or books are traditional in churches, at weddings, funerals, B&Bs, museums, schools, institutions and other private facilities open to the public. Some private homes keep visitors' books.
So that means.....
Its a place for logged in users to sign to say 'hello'.
Not a particular comment on something, just a "Hi there".