It may happen for some reason that SignIn page is missing in UMP Homepage.
Follow the steps below to get back SignIn portlet.
1.login UMP portal as administrator
2.go to Control Panel->Sites under Portal
3.click 'Actions' buton and select 'Go to Public Pages'
4.click 'Add' button and select 'Portlet'
5.click 'Tools' and add 'SignIn' portlet