Here is a sign I got out of the scrap pile on the ONR last year. sorry if it is sideways I could not grab the edited version. I do see mostly round holes or dots Identifying the crossings. reflective white on black background to contrast with the snow. I would see several variants while traveling, what I have seen the most. Sign post is always on the right side of the rail. There is a left and right flag on top forming a "V" to instruct the operator on which wing to pull in. Left side pull in the left plow for the obstruction on the left ahead such as a rock cut. No need to pull everything in.
see all three signs pull everything in as noted above, for a bridge or crossing.
I got to ride with a Jordan Spreader operator last year in Suie St. Marie last year on the G&W Huron line. He had run the machine for over twenty years. Everyone else though he was completely nuts to touch such a beast with all the loco's shoving behind him. He said they try not to take it out to much, they ran engines hourly to keep things clear. He would run it in the yard and clear 3 tracks at a time no problem.