This is a track direction/travel indicator. I don't think this is based on anything real, but it sort of looks like something you'd expect to see on a railroad. It helps me identify what direction the polarity of the track is, so I know which direction the trains will be going when coming to a junction.

It's easy to print, especially if you use the "One at a time" setting in Cura. There are two holes on the bottom of the main box STL. This is so you can put in a rod to help anchor the signal into the ground. I found mine kept getting knocked or blown over before I added stakes to them.

Here is a video I made showing how I wired one of these up. It's not a great how-to video, but it's the best I can offer right now.
https://youtu.be/f7YYemJ7ddU

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