Nocturnal CCTV works by flooding an area with invisible infrared light, which is true of the cheapest domestic CCTV to the stuff you see at military bases and corporate buildings. Anyone wishing to know when to smile for the camera should be able to detect infrared light.

The most basic way to detect infrared is with a small, inexpensive (<£10) strip that glows visibly when exposed to infrared. I have one sewn into my jacket sleeve, and it seems to work with bright infrared more noticably than with small infrared LED CCTVs. It illuminates surprising often walking through a city.

 http://www.mcmelectronics.com/product/72-6771
 http://cpc.farnell.com/IN02142/test-equipment/product.us0?sku=unbranded-72-6771