I agree that a "recording" light would be a great idea, but that will really only protect against malware, not against people who are intentionally trying to surreptitiously take pictures. The reason being that anyone with direct hardware access to the device can find a way to disable the light.

I think a recording light could be defeated by a tiny dot of suitably-colored opaque pigment dabbed onto the recording light. I prefer the earlier poster's thought of a sliding, readily visible lens cover.

The lens cover would defeat the whole purpose of having an at an instant camera. You may as well pull your cell phone out of your pocket if you have to fumble with removing a lens cover while you're wearing Glass. I understand why people are concerned, but I still believe through my own experience, that the issue is gratefully overblown.