Wis. Stat. § 46.298
Upon the request of a person who is certified as hearing impaired by the department, by a physician, by a hearing instrument specialist licensed under subch. I of ch. 459, or by an audiologist who is licensed under subch. II of ch. 459 or who holds a compact privilege under subch. III of ch. 459, the department shall issue to the person a decal or sticker for display on a motor vehicle owned or frequently operated by the person to apprise law enforcement officers of the fact that the vehicle is owned or operated by a hearing-impaired person. No charge shall be made for issuance of the decal or sticker. The department shall specify the design of the decal or sticker. The department shall designate the location on the vehicle at which the decal or sticker shall be affixed by its own adhesive.
Wis. Stat. § 46.298