My take:

KEEP THIS DOOR
CLOSED WHEN NOT
WEIGHING CARS

An important ancillary building once found in nearly every yard, but now less common, was the scale house.

Most cars containing bulk commodities such as grain, coal, and such were weighed - both to determine the weight for transportation charges by the railroad, and often for the charges the shipper would bill their customer for the merchandise. Every car had (has) the empty weight of the car stenciled on the side of the car, and the switching crew and a clerk would weigh each car, and subtract the Lt Wt (Light Weight, as stenciled) to determine the weight of the contents, and attach the scale ticket to the Bill of Lading.

Note that there are four rails past the scale house. The Live Rails were for weighing the cars, the Dead Rails (or Bypass Rails) were so that engines could pass the scale without using the Live Rails, since their weight often exceeded the capacity of the scale.

Mr. Delano was looking back from the caboose of a westbound train; the view is actually NNE. Des Plaines River/Sanitary and Ship Canal to the left, EJ&E bridge and Joliet Coke Plant in the background.

That looks like a train order signal. Not motorized, each blade appears to be manually operated by means of a pipe that extends down each side of the mast to just above the ground and then... nowhere. No trackside racks for delivering orders/messages on the fly, no telegraph office visible... are there any Santa Fe experts out there who know what this signal might have been for?

Keep the door closed when ??????????? cars.

[Illegible in the original. -tterrace]