回复：如果是parking ticket呢？那种警察留在车上的呢？要sign吗？

Not in California anyway. The same thing with red light camera tickets since nobody signs the ticket. For a regular ticket if you sign and fail to appear, you will be charged with failure to appear, a misdemeanor. The court can issue a warrant for your arrest or withhold your license. For redlight camera tickets, since you never promise to appear, technically the court cannot do the above. But it may take an appellate decision to settle this matter in law.