The bonds must:
(1) be negotiable;
(2) be signed by the county judge;
(3) be countersigned by the county clerk;
(4) be registered by the county treasurer;
(5) have the seal of the commissioners court impressed or printed on the bonds; and
(6) contain the following provision: "The holder hereof shall never have the right to demand payment thereof out of money raised or to be raised by taxation."