EBT Railroad signs *PIC*

These sound like one type of flanger signs. They indicated where flanger plows (which cleared snow from between the rail) had to be lifted to clear grade crossings, guard rails and other obstructions. Most western roads use a yellow triangle with a black dot to indicate the same thing.
I've never seen a photo of one on the EBT and assumed they did not use them. The EBT did not have a flanger per se', but they did (and still do) have a pilot mounted wedge plow that sets below the rail head. It would be appropriate to have flanger signs for that I guess.
I would be interested in any more info you have on the signs, such as what part of the line they came from.