Many times in the day police arrest individuals but the district attorney decides not to file criminal charges against them or decide to "reject" a request by law enforcement to bring a formal complaint against the accused. In these instances, the question becomes what affect will this have on my permanent record? It depends. If the person was booked, that is they were finger printed and a mug shot photograph was taken, then there will be an arrest record history sent to the California Department of Justice reflecting an arrest. Oftentimes, however, the police agency will not follow up on their duties and update the system that the person was not charged and that all criminal allegations were dropped. Without this critical step, the person may be strapped with the stigma of an arrest record that shows no disposition which could negatively impact employment and other important aspects of the person's life down the road. A lawyer can be retained to request that the record be destroyed or that proper methods should be adhered to so that the arrest is shown as a "detention only". This crucial follow up is overlooked many times and the arrestee will not be aware of the scar on his or her record.
One option is to formally demand that the police department issue a "certificate of detention" after the prosecutor fails to file formal charges. It should be noted though that this request may be a bad idea particularly when the D.A. is on the fence about filing charges. In these cases the police may take it upon themselves to pursue the case with the district attorney, sometimes called "awakening a sleeping giant". So be careful in how you handle these things, it is best to consult with an attorney familiar with the criminal laws in California.