Police in Los Angeles, and throughout the state of California, could potentially charge you with carrying a concealed firearm under a variety of circumstances. These types of weapons crimes could carry serious consequences if you were convicted.
To be clear, this law would probably not apply to any obvious weapons. A court would likely dismiss any charge of carrying a concealed firearm that involves open carry on a belt holster. Regardless of that fact, you would probably not want to argue with law enforcement about this charge until you secure a legal opinion on your case. California's gun laws are nuanced at best and complicated at worst.
The main law on the subject, section 24500 of the California penal code, defines carrying a concealed weapon as holding a hidden firearm on your person or in a vehicle you have control over. You could also be found guilty of carrying a concealed firearm if you hid a firearm in a vehicle while you were a passenger or occupant.
For example, police might claim probable cause and search your vehicle during a traffic stop. If they found a gun while searching your car, they might charge you with carrying a concealed firearm. If you and your defense attorney later established that the firearm did not belong to you and was hidden without your knowledge, a court might dismiss the concealed carry charge.
Regardless of the material situation, taking criminal charges seriously is often the best first step towards a complete defense. Therefore, please do not use this general information as legal advice for any case.