18 U.S.C. 1725
“Whoever knowingly and willfully deposits any mailable matter such as statements of accounts, circulars, sale bills, or other like matter, on which no postage has been paid, in any letter box established, approved, or accepted by the Postal Service for the receipt or delivery of mail matter on any mail route with intent to avoid payment of lawful postage thereon, shall for each such offense be fined under this title.”
Ironically, putting a copy of “the law” in the lady’s mailbox is itself a violation of federal law.
I think there is a possible fine of $100 if you do not provide information. If you provide false information, the fine goes up to maybe $500.