Utility to find out the SID of an account or a computer name

SID stands for Security Identification and it is used by Windows to uniquely identify Windows objects such as computer names, user accounts, security groups on a domain, etc.

Sysinternals has an utility called PsGetSid to view a machine’s SID by running it with no command-line arguments:

PsGetSID translates SIDs to names and vice-versa
You can download the utility from technet

An in-depth discussion of SID can be found here:

Mark Russinovich