Neb. Rev. Stat. § 60-399

(1) Except as otherwise specifically provided, no person shall operate or park or cause to be operated or parked a motor vehicle or tow or park or cause to be towed or parked a trailer on the highways unless such motor vehicle or trailer has displayed the proper number of plates as required in the Motor Vehicle Registration Act. (2) In each registration period in which new license plates are not issued, previously issued license plates shall have affixed thereto the validation decals issued pursuant to section 60-3,101 . In all cases such license plates shall be securely fastened in an upright position to the motor vehicle or trailer so as to prevent such plates from swinging and at a minimum distance of twelve inches from the ground to the bottom of the license plate. No person shall attach to or display on such motor vehicle or trailer any (a) license plate or registration certificate other than as assigned to it for the current registration period, (b) fictitious or altered license plates or registration certificate, (c) license plates or registration certificate that has been canceled by the department, or (d) license plates lacking current validation decals. (3) All letters, numbers, printing, writing, and other identification marks upon such plates and certificate shall be kept clear and distinct and free from grease, dust, or other blurring matter, so that they shall be plainly visible at all times during daylight and under artificial light in the nighttime. (4) Addition, removal, or modification of design, color, or appearance of any such license plate is prohibited while it is displayed on the vehicle to which it is assigned.