New Jersey Statutes Title 39. Motor Vehicles and Traffic Regulation 39 § 4-183.3

No person shall place, maintain or display upon or in view of any highway, any unauthorized traffic sign, device or other contrivance which purports to be or is an imitation of or of such a nature as to be mistaken for an official traffic sign or which attempts to direct the movement of traffic or which hides from view or interferes with the effectiveness of any official traffic sign and no person shall place or maintain, nor shall any public authority permit upon any highway, any traffic sign or signal bearing thereon or its support, any commercial advertising.

This shall not be deemed to prohibit the erection upon private property adjacent to highways of signs giving useful directional information and of a type that cannot be mistaken for official signs.