I’m not aware of any law in any state that proscribes telling other people about the presence of a uniformed police officer, whether the officer is doing speed enforcement or anything else. Cell phones, truckers on CB radios, even waves out the window have been used for years to warn of what you call speed traps.

However, there are laws in some states against flashing your lights or, more specifically, failing to dim your high beams for oncoming traffic. Vermont does not have either one of these laws. If you were to flash your high beams to warn other drivers and an officer in one of these states saw it, it is probably going to annoy the officer (yes, we get annoyed) because he knows the real reason you are doing it. The officer may pull you over and give you a ticket for inappropriately using your lights, if such a law exists. Personally, I think flashing each other to warn speeders to slow down is great, because it takes the enforcement effort of the officer and multiplies it exponentially.

Now on to your next question. The primary purpose of speed enforcement, and all traffic enforcement for that matter, is to reduce accidents and injuries and promote the smooth and efficient flow of traffic on our streets. A secondary benefit is that it gets officers out into the public contacting citizens, albeit in an enforcement setting, which is a good thing. Finally, it is a revenue generator. There is no denying that part of traffic enforcement and writing tickets is generating revenue, but that is not the main goal. If you look at the state and town budgets, it even has a line item under revenue.