"...minute stone or clay discs with a loop at the back, engraved with straight lines or criss-cross patterns. These objects, probably worn on a string around the neck, may have been impressed as a mark of ownership on lumps of clay fastened to baskets or to jar stoppers, in which case they would represent the earliest examples of the stamp-seal, and the stamp-seal is the forerunner of the cylinder-seal, a significant element of Mesopotamian civilization."
Georges Roux, Ancient Iraq, p. 51. Section titled, "The Hassuna Period."
(Citation for "Between the Rivers, Before the State.")