On the other hand while an indicator light is good for the camera, it's not sufficient for audio. If the computer is facing away from me, then the camera can't see me so my inability to see the camera light isn't that huge of a deal. But audio goes around corners so I could be recorded by a computer not immediately in eyesight.
If there were some reasonable third sensory channel to available for "out of band" communication, that would be ideal. But consumers will reject smell-alerts.