Wis. Stat. § 422.304: Prohibition of blank writings.

(1) Every writing evidencing a consumer credit transaction shall be completed as to all essential provisions prior to the signing thereof by the parties, and no creditor shall induce, encourage or otherwise permit the customer to sign a writing containing blank spaces which are to be filled in after it is signed except for a space provided for the identifying numbers of goods if not available at the time of the transaction. Blanks relating to price, charges or terms of payment which are inapplicable to a transaction must be filled in a manner which reveals their inapplicability unless their inapplicability is clearly and conspicuously indicated.

(2) A violation of this section is subject to s. 425.304.