Well, I'd only previously seen it on the gon, so this deepens the mystery bit.
As Mal mentioned, when I said I would do the graphic, I assumed it was some sort of "Iron Cross" symbol and was prepared to draw it that way and it wasn't until I blew up the photo to get a sense of the proportions, I discovered it wasn't any of the common crosses I would have assumed.
With this photo in mind, is it possible this is some sort of trust mark? A number of cars in this era had "CRS Trust" stenciled on the cars in Colorado. I don't have much info on the D&RGW (Utah narrow gauge era), so I'll throw that out there.
Chris Lane