Under no circumstances shall any revenue bonds or certificates issued by a regional metropolitan transit authority or any other obligation of such authority be or become an indebtedness or obligation of the State of Nebraska, or of any other political subdivision or body corporate and politic or of any municipality within the state, nor shall any such revenue bond, certificate, or obligation be or become an indebtedness of the authority within the purview of any constitutional limitation or provision, and it shall be plainly stated on the face of each revenue bond and certificate that it does not constitute such an indebtedness or obligation but is payable solely from revenue and income and other sources of revenue of such authority as provided in subsection (3) of section 18-815.