Technically, the prosecution for VC 22349(b) is required to prove "not a speed trap", but the definition of "speed trap" (in VC 40802) says a speed trap is a particular section of highway where ...Quoting JackA
- ... speed is measured by clocking the time a vehicle travels the section, or
- ... the speed limit is established by VC 22353(a)(2)(A): 25 mph in business or residential area, or
- ... the speed limit is established by VC 22357: increasing limit from 25 mph by E&T survey*, or
- ... the speed limit is established by VC 22358: decreasing limit from 65 mph by E&T survey, or
- ... the speed limit is established by VC 22358.3: decreasing limit from 25 mph by E&T survey
*"E&T survey" = "engineering and traffic survey".
But in your case, the speed limit is established by VC 22349(b), so it is a matter of law that the evidence or testimony presented is not based on a speed trap. Since it is law, the prosecution does not have to point that out to the judge; the judge already knows that.
As for advice for your case, one tactic you can try is when you are called to contest your ticket, if you know the judge to be a "hanging" judge, you can file a peremptory challenge saying you do not want that judge to try your case. They are required to reschedule your trial with a different judge. The book Fight Your Ticket & Win in California can tell you how to do that.
The advantage of this is that you double your chances of the officer not showing up.
An another tactic is to challenge the calibration of the speedometer of the officer's vehicle. See the above book.
VC 22349(c) is pertinent.Quoting JackA
However, the California Department of Transportation Traffic Manual has declared "reasonable signing" to be every 10 miles.

