Thats annoying. Please, fix that.

Prior to #8688, there was a setting for choosing the default signal type when starting a new game, after which the GUI keeps the last-used signal selected. It did not remember the last-used signal between games.

This setting was removed in #8688 as part of a general simplification of signal-related settings, and now it defaults to one-way PBS when starting a game, then remembers the last-used signal as before.

I As an admin server on which both advanced players and new players play, I can say that after the update, everything (including new ones) is in misunderstanding of the changes, and in search of signals. So far, I have seen the exact opposite of simplifying the game for beginners, as I see these beginners looking for help to turn on. And I don't understand why a handful of clever people solves what most people need by covering up their desires and whims with beginners.

It does not remember, It cannot remember. I searched thorugh the code. You just removed the setting that does it. In some function instead of "look in config and choose signal" it makes "always select one-way PBS".

If you read the diff carefully, you see that _default_signal_type is a "read-only" settings. That is to say: it is only read by the code, and never set (with the exception of the settings menu). In yet other words: it doesn't remember your last signal type used, but you can set what the default is when opening it.
Sounds you experience Mandela Effect :) If you don't believe me, try it out yourself in 1.11 or something. You will see you always start with the same signal type, no matter how you left it behind.

That said, I guess we could read the bug report as: "I want a way to set my default signal to either one-way or two-way". That was possible pre-12.0, and is no longer. I currently have no opinion on that :)

It's not the same bug, but it seems the root of the problem is the same, so I'm writing here.
Removing the setting also means that when running different versions of the game, each time the selected signaling setting changes. Sometimes both settings. If someone uses different versions for some reason (e.g. playing on different servers), each time before or during the game has to correct these settings. This is discouraging... :/