(a) A county or municipality may not remove an outdoor sign which is adjacent to an interstate highway and which was lawfully erected and maintained under State law and in existence or in litigation on or after November 6, 1978 unless just compensation is paid by the Administration.
(b) The Administration is not required to spend any funds under this section until appropriate matching federal funds are available to the State.
(c) The provisions of subsection (a) of this section shall not apply to any outdoor sign which is not eligible for matching federal funds.