Wis. Stat. § 344.30: Methods of giving proof of financial responsibility.

Whenever a person is required under ch. 343 or this chapter to give proof of financial responsibility for the future, such proof may be given by filing:

(1) Certification of insurance as provided in s. 344.31; or

(2) A bond as provided in s. 344.36; or

(3) A certificate of deposit of money or securities as provided in s. 344.37; or

(4) A certificate of self-insurance as provided in s. 344.16, supplemented by an agreement by the self-insurer that, with respect to accidents occurring while the certificate is in force, the self-insurer will pay the same amounts that an insurer would have been obligated to pay under a motor vehicle liability policy if it had issued such a policy to such self-insurer.