Wis. Stat. § 944.25: Sending obscene or sexually explicit electronic messages.

(1) In this section:

(a) “Electronic mail solicitation” means an electronic mail message, including any attached program or document, that is sent for the purpose of encouraging a person to purchase property, goods, or services.

(b) “Obscene material” has the meaning given in s. 944.21 (2) (c).

(c) “Sexually explicit conduct” has the meaning given in s. 948.01 (7).

(2) Whoever sends an unsolicited electronic mail solicitation to a person that contains obscene material or a depiction of sexually explicit conduct without including the words “ADULT ADVERTISEMENT” in the subject line of the electronic mail solicitation is guilty of a Class A misdemeanor.