Use the DSPSBSD command for QINTER (or any other subsystem) and select option 1 Display Operational Attributes. That will display the current Sign-on display file.
The simplest review of subsystems might be through the WRKSBS command. The command will bring up a list of all active subsystems on the system. From there, you can get into the jobs running in each subsystem or into the description of each subsystem.
An attribute of a subsystem description is the signon display file that is to be used for the subsystem. From the WRKSBS list, enter option 5=’Display subsystem description’ to access a menu of elements associated with any active subsystem. Menu option 1 is the ‘Operational attributes’. That’s where you can see which display file is to be used for that subsystem.
You can also reach the menu for an individual subsystem with the DSPSBSD command. You can use the CHGSBSD command to change a subsystem description.
Note that all four of your signon displays could be in use at the same time by four different subsystems.
Ideally, you would have at least one test subsystem that you could start and end whenever you chose. If you modified a signon display, you would test the display by associating it with your test subsystem first and signing on to it.