Powder River Basin Marker Panel

Hi All not sure if any railway folk out there familiar with operations in the Powder River Basin hang around this forum but i sure would like to know what the green panel on that post means https://www.flickr.com/photos/ycsfsoya/36598717170/in/album-72157688488679155/ Pretty sure there is a mile post just to the right of that so if any one has any info on the green panel thingy I would be most grateful.
Cheers Mick.

http://www.google.com/url?sa=t&rct=...%20Rules.pdf&usg=AOvVaw37RlBlQ3a3b86LO_S6ILx6
Looks like a permanent speed restriction sign

PERMANENT RESUME SPEED SIGN
Once the entire train has passed this sign resume the indicated speed,
or authorized maximum track speed if no speed is indicated. If two
numbers are displayed, the greater one applies to trains consisting entirely
of passenger equipment, and the other one applies to all other trains.

Or: GREEN FLAG (SIGN)
One or more temporary speed restrictions ends at this point.
Resume maximum permissible speed once the end of the train
has passed this sign.

Interesting considering that the PRB is BNSF track and UP just has trackage rights over it so they must just both use the same rules then, Thanks Cascade.
Cheers Mick.