Analysis of information sources in references of the Wikipedia article "Vehicle license plates of the United States" in English language version.
Every motor vehicle or trailer registered under this chapter when operated in or on any way in this commonwealth shall have its register number displayed conspicuously thereon by the number plates furnished by the registrar [...] one number plate to be attached at the front and one at the rear of said motor vehicle, and one number plate to be attached at the rear of said trailer, but if the registrar issues but one number plate it shall be attached to the rear of the vehicle so that it shall always be plainly visible.