Section 11-2113. Effect of posting or service of notice

1.  No  person  shall  enter  or  remain  unlawfully  or engage in any
  activity upon land which has been posted pursuant to section 11-2111  in
  violation  of the terms of such posted signs or the terms of any written
  notice and warning served upon such person pursuant to subdivision  four
  of section 11-2111.
    2. No person shall post any sign prohibiting or limiting activities on
  land  pursuant to this article, unless authorized to do so by the owner,
  lawful occupant or other person or organization having authority to post
  such lands.
    3. No unauthorized person shall injure, conceal, deface  or  remove  a
  sign erected and maintained as provided in section 11-2111.