If it's a rental or tourist-lease, the company will get the ticket and charge you. If it's a foreign-registered vehicle, well, just wait and see. Whereas the key first threshold for police officers who might write a ticket on the spot is reported to be a speed 10 percent over the limit, it's said that along highways the cameras are only triggered by vehicles going more than 20 kph over. Furthermore, it's rumored only half the photos are unambiguous enough to result in a ticket. If you trigger one of these cameras you'll probably see the flash.
Signs usually warn drivers if such an apparatus is permanently mounted along or above the road.
But often they're mounted in unmarked police cars parked on the roadside or median, and in such case of course no signs attend.