Wis. Stat. § 349.09: Authority to remove prohibited signs or signals.

Every sign, signal, pavement marking, or device which is placed, maintained, or displayed in violation of s. 346.41 is declared to be a public nuisance. The authority in charge of maintenance of the highway in question may notify in writing the owner or occupant of the premises upon which the nuisance exists or the person causing or maintaining the nuisance to remove the same. If such nuisance is not removed within 30 days after such notice is given or if an unauthorized signal or device is found to be in operation at any time after such notice is given, the authority in charge of maintenance of the highway may cause the nuisance to be removed and collect the expense of removal from the person notified to remove it. The expense of removal may be charged against the premises and, upon certificate of the highway authority causing the removal, assessed as are other special taxes.