This article talks about sprays. I’ve heard about using clear high gloss fingernail polish. No idea if it works or if it is legal in CA.
Britons are vandalizing the country’s growing army of speed surveillance cameras. The government has set up thousands of cameras to catch speeders; one vigilante group alone claims to have damaged more than 1,000. Favored techniques: “digging them up; shooting, hammering and firebombing them.” – slate