Wis. Stat. § 857.015
A spouse who holds property described under s. 766.70 (3) (a), (aL), (b), or (d) which is not also held by the other spouse may direct in a will or other signed writing that the marital property interest of the nonholding spouse in such property be satisfied as provided under s. 861.015. The holding spouse shall identify in a will or other signed writing the property described under s. 766.70 (3) (a), (aL), (b), or (d) to which the directive applies. The signature of the holding spouse on a directive other than a will shall be acknowledged, attested or witnessed under ch. 140. The estate of the holding spouse may not execute a directive under this section. If at the death of a spouse the surviving spouse is the holding spouse, the surviving spouse may execute a directive under this section if executed within 90 days after the decedent spouse's death.
Wis. Stat. § 857.015