This happened today in San Diego, CA. Here is the intersection: https://goo.gl/maps/FgKHyVVxQ2E2 (the satellite view is out of date; the construction is finished now and can be seen in Google Street View).
I had left the shopping center southwest of the intersection and was traveling north on Paseo Del Sur. I stopped at the intersection with Camino Del Sur and observed that cars were making left-hand turns from westbound Camino Del Sur onto southbound Paseo Del Sur. There was one car on Paseo Del Sur in front of me, and it made a right turn. I pulled forward and stopped at the intersection. Vehicles were still making left turns, and none were making U-turns, so I made a right turn. About 50 yards ahead of me on Camino Del Sur was a police car, parked on the side of the road, with its flashers on. As I passed the police car, I saw another vehicle parked in front of it, as if the officer had made a traffic stop. In my rear-view mirror, I saw the police car merge into traffic. His flashers remained on as he followed me eastbound. He turned on his sirens briefly between Lone Quail Rd. and Dove Canyon Rd., and I pulled over immediately.
The (polite and respectful) SDPD officer issued a citation for CVC 21461(a), Violation of Signs:
21461. (a) It is unlawful for a driver of a vehicle to fail to obey a sign or signal defined as regulatory in the federal Manual on Uniform Traffic Control Devices, or a Department of Transportation approved supplement to that manual of a regulatory nature erected or maintained to enhance traffic safety and operations or to indicate and carry out the provisions of this code or a local traffic ordinance or resolution adopted pursuant to a local traffic ordinance, or to fail to obey a device erected or maintained by lawful authority of a public body or official.
Apparently I violated "No Right Turn on Red" signs. At the time I didn't see them, but they've visible on Google Street View: There is one on Paseo Del Sur maybe 15 ft before the intersection, as well as one about 100 ft away across the intersection (over the road sign for Camino Del Sur). The officer told me that they've had numerous accidents with people turning right on red, which is why he's enforcing the sign today.
I can think of three defenses (which I believe can be used in tandem):
- The officer could not have observed me violating the law. I did not observe him out of his vehicle. Since he was in his vehicle the whole time, he would have been facing forward (eastbound). If he was looking behind himself at all, his view was too obstructed to clearly observe me.
- The officer was not paying enough attention to turn off his flashers. It is reasonable to believe he was not paying enough attention to observe me.
- The signs are not clearly visible. The sign before the intersection is too far back, while the sign across the intersection is too small.
Do I have any hope of prevailing with these arguments, or would it be a waste of time? I suspect that if I do go to trial, the officer will be there (since this enforcement was planned).

