EnhGUIWindow

This is what it looks like:

You can access it from the toolbox menu in TTD.

Station signs

Here you can choose transparent or regular, "TTD style" station signs.

Depot Size

This sets the width of the train depot windows.

Depot allTrash

When enabled, this means everything in a depot outside the main train list area will act like the trash bin. You can then sell train vehicles by moving them onto the title bar for example.

Stick Settings

Save these settings with the current game. Only works if "saveoptionaldata is on".

Unstick

Remove these settings from being save with the current game.

Save as default

Make these settings apply to all games which haven't had settings saved with them.