These are Certificate-based SQL Server Logins

Server principals with names enclosed by double hash marks (##) are for internal system use only. The following principals are created from certificates when SQL Server is installed, and should not be deleted.

##MS_SQLResourceSigningCertificate##

##MS_SQLReplicationSigningCertificate##

##MS_SQLAuthenticatorCertificate##

##MS_AgentSigningCertificate##

##MS_PolicyEventProcessingLogin##

##MS_PolicySigningCertificate##

##MS_PolicyTsqlExecutionLogin##

http://msdn.microsoft.com/en-us/library/ms181127.aspx

Glad I could help!

MJ