Wis. Stat. § 114.19
The certificate of the license or permit respectively required of a pilot or a student shall be kept in the personal possession of the licensee or permittee when the licensee or permittee is operating an aircraft within this state. The certificate of the license required for an aircraft shall be carried in the aircraft at all times and shall be conspicuously posted therein in clear view of passengers. Such certificate of pilot's license, student's permit or aircraft license shall be presented for inspection upon the demand of any passenger, any peace officer of this state, any authorized official, or any official, manager or person in charge of any airport in this state upon which it shall land, or upon the reasonable request of any other person. In any criminal prosecution under any of the provisions of this chapter, a defendant who relies upon a license or permit of any kind shall have the burden of proving that he or she is properly licensed or is the possessor of a proper license or permit. The fact of nonissuance of such license or permit may be evidenced by a certificate signed by the official having power of issuance, or the official's deputy, under seal of office, stating that the official or deputy has made diligent search in the records of the official's office and that from the records it appears that no such license or permit was issued.
Wis. Stat. § 114.19