Power channel 'sw12empty' is controlled by the switcher, and activates the destroy sign. This destroys empty trains.
Right-clicking a node that has an assigned sign with a lever will open a dialog to add a new output power channel. In this dialog the name of the channel can be inputted, after which it is added to the sign. The sign will set the output channel the same way it would toggle a lever. For example, station signs toggle the channel on while a train is waiting on top, and switcher signs toggle it on when a matching train rides on top.
