Someone lives on a busy street and often people park in a way that makes his mailbox inaccessible. Parking on that street is not illegal. However there is a clear sign at the mailbox that they ignore. The sign says "Do not block mailbox". Notes put on the cars telling them to please not block the mailbox are ignored.
Moving the mailbox is not an option. The city is unwilling to put an enforceable No Parking sign at the location.
By American law it is illegal to block a mailbox. However it is not enforced to my knowledge.
Whoever knowingly and willfully obstructs or retards the passage of the mail, or any carrier or conveyance carrying the mail, shall be fined under this title or imprisoned not more than six months, or both.
(June 25, 1948, ch. 645, 62 Stat. 778; Pub. L. 103–322, title XXXIII, § 330016(1)(B), Sept. 13, 1994, 108 Stat. 2146.)
Is there anything a person can do to a repeat offender, Halachically, in such a situation?