30. " Valuable security".-- The words" valuable security" denote a document which is, or purports to be, a document whereby any legal right is created, extended, transferred, restricted, extinguished or released, or who hereby any person acknowledges that he lies under legal liability, or has not a certain legal right. Illustration A writes his name on the back of a bill of exchange. As the effect of this endorsement is to transfer the right to the bill to any person who may become the lawful holder of it, the endorsement is a" valuable security".