I found that by default in SharePoint 2013, there is no option for "Sign in as different user".
Introduction
I found that by default in SharePoint 2013, there is no
option for "Sign in as different
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"
