What should I do if I lock my car and don't inform the owner?

This is illegal and can be handled by the police.

They are not the administrative subject of the property department, so no matter what the name, they can't impose fines on the owners at will, such as locking cars and trailers, which have the nature of administrative punishment. Then, if the owner encounters such illegal acts of charging fees or locking the trailer, he can complain to the Urban Management Department of the Price Bureau of the local public security traffic police market supervision bureau, or call the public hotline 12345 and the preferential consumption hotline 123 15 to reflect the situation. If not, he can also bring a civil lawsuit to the court, demanding to stop the infringement and compensate for the losses. "