absence of signal is not a good indicator of operation. it is the same signal as total failure of your system.
In the early 1980s Airbus adopted Dark Cockpit where the default state of all annunciator lights is off. If one illuminates then it indicates something worthy of attention. The colour of illumination indicates functional state; blue is good, amber is malfunctional.
Of course, one might very well argue that 'turned on' is not 'worthy of attention'
[1] http://www.smartcockpit.com/docs/A330-A340_Overhead_Pushbutt...