For your guest, any kind of messages may be sent to them which are very important for your guest. If any known person of your guest wants to register his/her message, you should have to go with this path; Utility>Guest message.
A following window will appear to you as;
Once you fill up above message box you need to save for delivering it to your guest . After that your saved message automatically will be updated in the following window, which will tell you to deliver guest’s message. You will deliver this message by pressing Deliver key. In case if you miss to deliver guest message, you can check it by clicking on Show Undelivered Message Only. The window will exist there as;