Lifelong California resident here (51 years). I carried a fixed-blade for several years.
I liked Charlie Mike, but he had a tendency to push the envelope.
I used to carry my fixed-blade with the sheathed portion of the blade covered by clothing and only the handle showing, but my attorney, who was very knowledgeable on knife laws, and pro-knife, convinced me to carry my knife in such a manner that it was completely visible from the tip of the handle to the blade-tip of the sheath.
Also, he convinced me (as did a friendly encounter with the cops) to carry in such a way that it is impossible for clothing to accidentally cover the knife.
There is a superior court decision here in California that defines a "concealed" fixed-blade by the intent of the carrier. Meaning- was it the intent of the carrier to conceal the knife from view? And people are supposed to be in the clear if their knife becomes accidentally, temporarily covered by clothing. But my attorney reminded me that the cop on the street isn't likely to be familiar with that decision, and based on the officers personal perception you could be arrested and spend some time in jail before it gets sorted out (or not if a prosecutor wants to push the case).
In California carrying a concealed fixed-blade is known as a "wobbler". This is a legal term which means a crime that can be charged as a misdemeanor or a felony, a decision made by the prosecutor. And prosecutors ALWAYS charge the maximum.
When it comes to carrying a fixed-blade in public, and the chance of encountering a member of law enforcement, my advice is to make sure the entire sheathed knife remains fully visible at all times.