Guestbooks are a part of your Habbo User Page. People can leave messages on it.
As a result of a technical response to an issue in which guestbooks with over 1000 posts would cause the site to crash, [1] the guestbook post counter now shows >1000 if a guestbook exceeds 1000 posts. This was implemented on November 2009.
Spamming
Spamming three times within a minute can land you a ten-minute ban from signing anybodie's guestbook.