[Iska]

Можно:

Код:

@echo off
setlocal enableextensions enabledelayedexpansion

for /f "usebackq delims=" %%i in (
	`wmic.exe useraccount where "LocalAccount='True' and Name='%username%'" get SID /value ^|find.exe /i "SID"`
) do set "s%%i"

if defined sSID echo SID=%sSID%

endlocal
exit /b 0

NB! Не ниже Windows XP.