Code:
on *:appactive: {
  /.timerappactive 1 1 /appstate $appstate
}

alias appstate {
  if ($1 == minimized) { /set %AwayStatus Yes | echo -s %AwayStatus $appstate }
  if ($1 == maximized) { /set %AwayStatus No | echo -s %AwayStatus $appstate }
}


Minimize mIRC, then maximize it. Check the status window..

Yes minimized
Yes maximized