70 ILCS 1510/12

All bonds issued under the Project Sections have a lien upon the income and revenues derived by the Chicago Park District with respect to the project for which the bonds have been issued, and the ordinance authorizing such bonds may provide for the issuance of additional bonds to be equally and ratably secured by a lien upon such income and revenues or may provide that the lien upon such income and revenues for future bonds is subordinate.