We have all seen mile markers, yard limit signs, even markers to signal horn blowing, but these are new to me. Yesterday, I watched a pair of GP40’s deliver 2 covered hoppers to Arizona Grain. While running down the siding, the Geeps were stopping, waiting for the crossing gates to lower, and then rolling through the street. I noticed as I pulled away, a rectangular red sign that said STOP. Taking train pictures all my life, and I missed this detail?