RE 3 Bars - I expect that is "functional design" - make the MIC/TRANSMIT selection buttons quickly distinguishable from all the other pedestal lights/buttons at night.
Alternatively - could be simply 3 LEDS for redundancy, in case one burns out. But the fact that the pattern (3 bars, regardless of orientation) is common across B and A makes the first idea more likely. Embraer uses one bar - but still a bar (EMB reception controls have round indicator lights).