Trackside Cross

Today I was asked a question about a trackside marker. It was described to me as this:

  1. Posted next to the tracks.

  2. Approximately 5 feet in height

  3. Shape of a cross

  4. The letter ‘B’ on the cross

“B” for “Block”, as in the start of a block or the end of a block?

I can’t think of anything else. And I’m not sure why a cross shape when a simple post would do.

Perhaps this is it:

https://www.youtube.com/watch?v=r6s4gOvoEgo