Ala. Code § 2-6-119
In the proceedings authorizing the issuance of any of its bonds, the corporation is authorized and empowered to pledge for the payment of the principal of and interest on bonds at the respective maturities of the principal and interest, and to agree to use solely for such purpose, all the revenues which under the provisions of Section 2-6-118 are provided for the payment of the principal and interest, subject to prior pledges as and to the extent the corporation may provide. Upon the issuance of any bonds pursuant to this article, the corporation may file in the office of the Judge of Probate of Montgomery County, Alabama, an instrument reciting the issuance of the bonds and the pledge of the revenues as security, and the filing of the instrument shall constitute constructive notice of the pledge. The instrument shall be received and recorded by the judge of probate upon the payment of the fee for the recording of mortgages, but no tax shall be payable.
Ala. Code § 2-6-119 (1975)