This policy setting controls whether the specified 2007 Office applications notify users when unsigned application add-ins are loaded or silently disable such add-ins without notification.If you enable this policy setting, applications automatically disable unsigned add-ins without informing the users.
If you disable or do not configure this policy setting, if an application is configured to require that all add-ins be signed by a trusted publisher, any unsigned add-ins the application loads will be disabled and the application will display the Trust Bar at the top of the active window. The Trust Bar contains a message that informs users about the unsigned add-in.
This policy setting only applies if the 2007 Office application is configured to require that all add-ins are signed by a trusted publisher. By default, users can configure this requirement themselves in the "Add-ins" category of the Trust Center for the application. To enforce this requirement, you must enable the "Require that application add-ins are signed by Trusted Publisher" policy setting in Group Policy, which prevents users from changing the setting themselves.