Base for signal light ?

[backwoods tracker]

Today my wife and I were scouting out an area along a railroad track . We found 20 insulators , an old rivet, and pin. We also found the item pictured here. It is made of cast. The nipple is threaded and inside is a wire contact. On the other side is what appears to be a bulb contact. I am assuming this is the base of an old railroad signal light of some kind, but am not sure of the exact function, or era from which it came.
On the outside there are two stamps, one of which is D 2, and the other is 1432462.

Anybody familiar with this ?

 

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[Helix]

What does the back side look like.

 

[backwoods tracker]

What does the back side look like.

Here is the inside. It has a contact with a rubber insulating disk.

 

[Helix]

Looks like one of those porcelain light bulb fixtures you see but metal. I think you might be right on it being some kind of light fixture of some sort.

 

[backwoods tracker]

Yeah. It's made of cast iron, and we found it right next to the train tracks in the middle of nowhere. Pretty sure it is railroad related and definitely from some kind of signal or marker lamp.