It's worth noting that signs are not always visible with sufficient distance to change speed before them.
The laws here state that you're supposed to have time after a change of limit sign to adjust speed before you can be fined.
In that case it was a suburban area that entered a shopping strip and the signs had recently been changed. It used to be 60 along the whole stretch.
The 50 sign was not visible until you were very close to it.
With speeding tickets here you are assumed at fault unless you can prove otherwise, so despite the fact these things had changed and there was no signage to indicate that, and also the sign was not visible until too close, and that my speed was acceptable by the legal distance after the sign, the cost to dispute it without being sure of victory (and costs) was prohibitive for me at the time - this was years ago.
Beside that, I said it was harsh, and believe it was, but I paid the fine and don't gripe about it because it was an unmarked car. In that stretch braking would have been unsafe and I would have done the same with a marked car behind.
Thing is though, marked cars almost never pull you over for that stuff, because they actually have priorities other than revenue.
Given that I didn't actually break a law, and they waited until well after I was at the right speed before pulling me over, it was a quota system in play and they were under quota and I just happened to be in the wrong place at the wrong time.
I object in principle to the unmarked cars, my ticket was just an example of how they are sometimes misused. But even beside that misuse, they are still a waste of police resources, and I objected to them long before my own personal experience with them.