You can see who has visited your registry and signed your Guestbook when you login to your account and hover over Settings located at the top of the page. From there select the Guestbook option from the drop down menu. Furthermore, you can disable/enable the Guestbook by hovering over Settings at the top of your page to select Visitor Set Up. From there, click the slider button from the Guestbook section to disable/enable this feature.