I assume you mean being able to turn a System Maintenance message on / off for users so they see the message when they log in.
On way is:
1) Create a VP called VP_Maint that has the content and menu options you would like on your maintenance message
2) Create attribute: SystemSetting.MaintFlag - Yes / No type
3) Create a process called: Maint_Check as follows:
If SystemSettings.MaintFlag='Yes' Then
DISPLAY PERSPECTIVE VP_Maint
ELSE
DISPLAY PERSPECTIVE Administrator
4) On login VP, click on the General tab & in the section "Run initialization process", select the process from #3 above.
