... all we need is some way to accomplish camera-jamming... anyone got a remote for that?
One could always build an array of infrared LEDs and point it at the camera or use laser pointer. It won't turn the camera off but it will tweak/blind the ccd/cmos. The image will show a bright light but the human eye will not notice it for the LEDs, for the laser you are on your own to experiment with.

One could build a flashlight and point it at the cameras for grins. Some college chums used to build these LED flashers to force a green light while at stop lights. However, this is now a crime in the U.S. (
http://www.wired.com/science/discoveries/news/2005/08/68507) and would not be recommended for vehicular use.

Why would anyone drive 80mph through an intersection?
Before I get sidetracked, one could see what I am getting at by using your digital camera (cell phone or stand-alone) and pointing a television, DVD, VCR remote at it and pushing a button on the remote. You'll notice the flashing light on the camera but not with your naked eye.

None of this is an "off switch" more of an annoyance and possibly entertaining.
If all else fails, slap the old sticker on it or use sand paper on the lens. Cheaper camera boxes and many PTZ cameras use materials susceptible to abrasive countermeasures. Ultimately it all hinges on how bad one wants to be. Please make sure none of this will get you in trouble with the law, it'd only be one more place for the Evergreen's of the world to gather more information on you.
Enjoy!