I am generally weary of government regulation, but, depending on the implementation, I might be onboard with a law that requires cameras and microphones to have a power indicator. Specifically, the LED should be hard-wired into the main power wire going into the camera/mic, so that it will activate any time those sensors are receiving electricity.
Hence all cameras must make powerful low-frequency vibration when active.
Such a law should be equally applied to police body cameras.
Cops frequently have to chase suspects into dark areas. Being lit up will both help suspects get away easier and massively increase the risk that the suspects will be able to easily shoot their pursuers.
They're either in cars or if they're patrolling on foot (which is basically only something that happens in very dense commercial areas), they're dressed to be obvious and noticable. That's the mechanism by which police can prevent/displace crime: would-be perpetrators see police and choose to wait, commit their crime elsewhere, or (potentially) cool off and not commit the crime.