"Sign in as Different User" menu option is missing in SharePoint Server 2013

1. Locate and then open the following file in a text editor:  C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\TEMPLATE\CONTROLTEMPLATES\Welcome.ascx
2. Add the following element before the existing "ID_RequestAccess" element:
   <SharePoint:MenuItemTemplate runat="server" ID="ID_LoginAsDifferentUser" Text="<%$Resources:wss,personalactions_loginasdifferentuser%>" Description="<%$Resources:wss,personalactions_loginasdifferentuserdescription%>" MenuGroupId="100" Sequence="100" UseShortId="true" />
3. Save the file.

Now you can see "Sign in as Different User" option.