Pressing the "S” button changes between the respective output groups (A-D, E-H, etc.). After each change, the respective channel signals whether it has been parametrized as a Switch Actuator or as a Shutter Actuator in ETS. If the LEDs of a channel (up + down) flash at a frequency of 5 Hz, this signals Shutter mode. This brief indicating signal soon stops again, however.
If the channels are parametrized as a Switch Actuator, there is no flashing signal.
Information about this and many more valuable tips can be found in the manual for Combi Actuators at:
Link to manual