Red Light Camera Signs

A somewhat recent phenomenon in Houston, Texas is the use of red light cameras at certain intersections. Now, I have no complaint about the use of these cameras. I actually have a good laugh each time I see one of the cameras flash when some idiot runs a red light. However, what I cannot really understand is why they actually put up signs warning people where the red light cameras are located.

Isn't the point of the red light cameras to catch people breaking the law, catch people running red lights? Or is the point of the cameras to truly just stop people from running the lights out of fear of receiving a ticket? If the former is true, why alert people to where it is safe and unsafe to break the law? Really, is having these red light camera signs really that different than if banks had signs outside saying "Armed Undercover Police on Patrol Inside"? The bank robber, if believing this sign to be true, would just move on to a bank that does not have one of these signs. However, if the manager of a bank realizes that robbers are less likely to rob a bank if such a sign is present, why wouldn't the manager just put up such a sign irrespective of whether undercover police actually patrolled the bank? This question goes to addressing the second possible reason for the red light cameras that I mentioned above. If you just wanted to stop people from running red lights out of fear, why not just put up the signs everywhere irrespective of whether cameras are located there are not? Is it that the belief is that people will figure out which of the intersections really have cameras and will stop where the real cameras are and continue to run lights where cameras do not really exist? If this was the thought process behind putting up the signs, then congratulations, this seems to make sense...sort of. But this begs the following question: why do we have red light cameras?