here in az they did determine that these radar enforcement zones are for revenue enhancement and they have been prohibited by state law. As the op noted there is a small sign placed 50 ft or so prior to the enforcement vehicle and they already have your picture.
For the holier than thou speed limits are not for safety per se, as many roadways have been determined to be posted at lower speeds than are safe. Makes ya think does it not. We had a roadway posted at 35, lotsa tickets, state got involved in court case and engineers determined that 55 was an appropriate speed for the roadway. In Ok 1 time I crossed a street and had been in a 35 speed zone, crossed the other street and it DROPPED to 25 with no notice! Got a ticket, when I asked the cop where was it posted he claimed that it was on a sign at the CITY LIMITS but could not tell me where! It was a LOCAL thing. Anyhow went to the court and it was dismissed as not even the judge could answer the question. Did find a sign some months later a small backroad but that was it. Too many Barney Fifes out there with a better idea.