Sets the text to display to incoming ssh (command-line shell) connections, if enabled. Note that the text is displayed before the login, so any connection - whether the login succeeds or not - will see the banner. The message could be a description of what the machine is/does, for those in the organization that have access to it.
This setting might not be available on older editions of the Search Appliance. Also, before using this setting, ensure that the Search Appliance software is up to date (System → System Setup → Update Software), especially thunderstonePatch.