Wis. Stat. § 347.495: Registration plate concealment device.

(1) In this section, “registration plate concealment device” means a manual, electronic, or mechanical device designed or adapted to be installed on a motor vehicle to do any of the following:

(a) Switch between 2 or more registration plates.

(b) Move, obstruct, or conceal a registration plate.

(c) Alter the appearance of a registration plate so that the registration number cannot be seen and read.

(2) No person may possess, sell, purchase, install, or use a registration plate concealment device.

(3) No motor vehicle may be equipped with a registration plate concealment device.

(4) Any motor vehicle equipped in violation of sub. (3) may be impounded. A vehicle impounded under this subsection shall be returned to the owner upon payment of reasonable costs of towing and impounding the vehicle.