Beyond Reasonable Doubt

首先，你不能提前contest，应该按时间去回应。

其次，第一次出庭仅仅是plea guilty还是not guilty，如果你plea not guilty, 具体庭审要等再次安排。所以五月份那次去，你也没有机会辩解。第一次出庭警察不会去，要等到庭审的时候警察才会出面作证。

至于你的问题，你的根据是那个路口，没有限时左拐的标志，只有限时右拐的标志。而警察抓你的理由，“cannot turn into this street". 是假设左拐右拐都有限时。如果你证据确凿，你可以试一试。可能那天标志掉了，不是没有可能。

关键词是“beyond reasonable doubt”。  The police did not prove beyond reasonable doubt that I violated traffic control device.  My pictures show that there was no traffic control device prohibiting left turn at the crossroad. 

CA Vehicle Code 

22101.  (a) The Department of Transportation or local authorities in
respect to highways under their respective jurisdictions, may cause
official traffic control devices to be placed or erected within or
adjacent to intersections to regulate or prohibit turning movements
at such intersections.
   (b) When turning movements are required at an intersection notice
of such requirement shall be given by erection of a sign, unless an
additional clearly marked traffic lane is provided for the approach
to the turning movement, in which event notice as applicable to such
additional traffic lane shall be given by any official traffic
control device.
   (c) When right- or left-hand turns are prohibited at an
intersection notice of such prohibition shall be given by erection of
a sign.
   (d) When official traffic control devices are placed as required
in subdivisions (b) or (c), it shall be unlawful for any driver of a
vehicle to disobey the directions of such official traffic control
devices.