I saw someone mention that the code for both block and path signals was in the game. So I found it. What I found was that not only is the code for both there, it’s the files labelled “block signal” which are being used. If you open up the block signal MDL you’ll notice that the name parameter is set to “path signal” and the mesh is set to the block mesh. If you change the name to block signal and check in game you’ll see it’s changed. You’ll also see that “path signal” has no name, but available from 1925.
There is also a crossing signal. I’m not sure how these can be activated.