For enabling this option need to follow below steps:-
1.Go to the Path Location:
C:\Program Files\Common Files\Microsoft shared\Webserver Extensions\15\TEMPLATE\CONTROLTEMPLATES Here a file named "welcome.ascx".
2.Open the welcome.ascx file in Visual Studio save it:
3. The tag that has Add below <SharePoint:MenuItemTemplate runat="server id="ID_PersonalInformation"
In this article we have explored SharePoint 2013 ""Sign in as different user" disable.. I hope this article we have enable and active.