回複：我住LA，那天去參加一個考試，出來時迷路了，到一個十字路口綠燈左轉，被拍了照，當時不明白為什麽？

you can say something like:

1) the sign is not obvious, it is so nonobvious that a reasonable person cannot see it or easily recognize it when they drive through. (if it was dark in the evening when you drove through, you should also mention it)

2) you were not familiar with that area. 

3) You have never intentionally violated any traffic rules. 

4) Combining factors 1, 2, 3 above, the court should reduce the fine.