Finding the local computer's machine account SID

The Get-ADComputer cmdlet, I hear, can get the SID of a computer's Active Directory machine account. But because it contacts Active Directory to look up the account, it won't work if not connected to the domain. If you have administrative privileges on the computer, you can elevate to SYSTEM (e.g. with PsExec) and get the computer's machine account SID from the default value in this Registry key:

HKLM\SECURITY\Policy\PolMachineAccountS

It's in binary SID format and so may be tricky to read by eye. If you just need the RID, that's the last four bytes, or you can get it as the only contents of the sister key PolMachineAccountR.