Disabling traffic enforcement cameras using paint

While we were in South Africa, many times we would slow down our car to avoid getting "snapped" by a speed camera. There were a few cameras close to our home, and these were a frequent source of irritation for us. We sometimes wondered - how to impair these cameras without causing damage to the devices?

A speed camera in South Africa (source)

After a few discussions, one seemingly good idea that hit our minds was coating the camera's lens with black paint - effectively blinding it - without causing any visible damage. This act should be done at night, so that the camera doesn't capture the perpetrator's face.

I wonder whether damaging/disabling/impairing traffic cameras is a frequent occurrence in the world.