747-400 Primary Flight Display indicator help.

Not gauges really, LED indicators is what I need help with.
Can anyone please teach me what an O M and another letter that flash in the Primary Flight Display? they appear between the red numbers that indicate the set FLT and IAS shortly after take off and just prior to landing. I can't find out what they are, what they are called and what they indicate...

Also, I would like to know if anyone knows how to completely shut off the 747-400 (stock version from fs9) I can turn engines and everything else off, except the Primary Flight display. I simply want the bird to get some sleep.

Must grateful, Gatortech2002

The Outer and Middle and sometimes Inner are Marker beacons indicators. These are ground based radio transmitters that positively indicate an aircrafts position on the Localizer during a instrument approach. When the light comes on, you know your exact position during the approach. They are installed in conjunction with the ILS or Localizer for instrument landing in poor visibility.
http://en.wikipedia.org/wiki/Instrument_Landing_System#Marker_beacons

Thank you explaining so well the meaning of these indicators.