If you new to SharePoint 2013 like me and get confused looking for “Sign in as a Different User” menu command, don’t worry it is not there by design but we can easily bring it back.
Do the following steps to get the link back:
Text="<%$Resources:wss,personalactions\_loginasdifferentuser%>"
Description="<%$Resources:wss,personalactions\_loginasdifferentuserdescription%>"
MenuGroupId="100"
Sequence="100"
UseShortId="true"
/>
Save and close the file. Now you should get the link “Sign in as Different User” back.