Basically anytime you see a car or van parked on the side of the road(perfectly perpendicular to the road)... you should take note.
Also... when you are speeding inside the city limits the penalty is much more severe than when your outside of the city limits(yellow city sign!). This is why I only speed "a little bit" when I am on the autobahn. And even then... not more than 20kph, bc after that it can get very expensive.
ALSO never speed when the autobahns change or intersect or when in a construction zone. When the speed drops to 80 kph or even 60 kph on the Autobahn, for sure there are cameras there. I also never speed when I know there is a football(soccer) game going on in the area. Thats like free money for the Polizei. How do you know a game is on that day? Just look for the soccer scarves hanging out of the car windows on the autobahn!