Add Sign in as different user Option in SharePoint 2013

Steps:

Go to the below Location

C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\CONTROLTEMPLATES

Look for the File Welcome.ascx

Open the file in Notepad , Add the Below Tag under completion of the tag "ID_PersonalInformation"


Syntax:

<SharePoint:MenuItemTemplate runat="server" ID="ID_LoginAsDifferentUser"
            Text="<%$Resources:wss,personalactions_loginasdifferentuser%>"
            Description="<%$Resources:wss,personalactions_loginasdifferentuserdescription%>"
            MenuGroupId="100"
            Sequence="100"  UseShortId="true"
             />

Note:Always take the backup of the  Welcome.ascx