Really simple question, that I can't seem to find a definitive answer for.
Does SharePoint 2013 support single sign-out?
If you really mean Single-Sign-Out, then the answer is no. SharePoint is a web application and when you log out of SharePoint you're only logged out of that application and not all other system relying on e.g. your domain account.
There is no "message" transferred from SharePoint to "all" other systems that you logged out. The other way around: Signle-Sign-On is supported if you're using Claims Authentication or NTLM to login.