A new California law starts 1/1/19 that requires paper license plates on all new and used cars (except private party sales). The new plates are valid for 3 months. Doesn't say anything about front plates specifically, but does talk about the "required" number of plates.
One of the reasons for the new law is to make cars easier to identify for law enforcement before they get their regular license plates, and to make it harder for toll road violators...
Temporary Paper License Plates
One of the reasons for the new law is to make cars easier to identify for law enforcement before they get their regular license plates, and to make it harder for toll road violators...
Temporary Paper License Plates