The authorized systems area lists all the hosts that are allowed access. The excluded systems area shows all those known hosts that are explicitly denied access. The graphic preceding the host name or IP address depicts what type of security is being used with that host.
A blank box preceding the host name indicates no encryption (Security = Off).
A box with a lock in it indicates that the system is using SKIP as the encryption method (Security = SKIP).
A box with the Sun Microsystems' logo in it indicates that the system is using SKIP Version 1 (Security = SKIP version 1).
A box with an N indicates a system that is Nomadic (that is, it is identified by its key ID not its IP address) and that it is using either SKIP or SKIP Version 1 as the security method.