for hide:
reg add "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v HideFastUserSwitching /t REG_DWORD /d 1 /f
===================
for show:
reg add "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v HideFastUserSwitching /t REG_DWORD /d 0 /f