Signing a guest book is read as leaving a mark of having been present. Dream books link it to wanting to be remembered and to the record of people who passed through your life.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.