I used to include a document with my signal pack that talked about these settings. This was about 10 years ago. Here is an excerpt from that manual.
As you can see there are two settings for Id, 1 and 2. These are used on the permissive signals as they have 2 signs attached to their posts. Each ID can be 4 digits. Id1 will show in the top sign and Id2 will show in the bottom sign. By default, if these are left blank the permissive signals will put the letter “P” on the top sign and “32/4” in the bottom sign. You may choose to use the ID for putting the mile marker on the post or some other text.
Below the ID’s are the lines for each link, in this example there are 2 links. Link 1 will be the straight-through route and link 2 covers the diverging route. In this example, the speed “Spd” column is not set for link 1 and is set to 15mph for link 2. Link 1 will use whatever speed the track is set to where the actual link is placed. This is how you set the speed limit for the junction. Link 0 will always use the track speed so set your track speeds.
There are two more boxes used on these signals, the “App” box and the “Limit” box. The “App” box stands for approach. You can set any signal to be an approach signal. You will ONLY set link 1 to use this setting. This tells the signal to act as an approach signal.
So, the new box you are showing, the top 2 boxes are ID1 and ID2. This changes the text on the singal signage. The next lines are for each link. Left to right. Character (not sure what this does as I never used it), Speed Box, Approach Signal, and Limit Signal. All of these options are dependent on how the signal is scripted and then where the type of signal is placed. I can only speak to the signals that I scripted long ago where I may have wanted to place an approach signal that would look ahead down the track to see what the next signal was set to. Usually that signal would only have 1 link as it doesn't cover a junction. The Limit option is similar but again only uses 1 link and you would apply a speed to it. This would then set the speed indication of the signal to something other than the track speed setting. The signal would never change its indication. Both The approach and Limit options are usually used for speed control, not used on a junction, and use only 1 link. The Approach will respond to the next signal's indication, the limit will only show the aspect for the speed indicated in box for the link and it never changes.