Ancient kings sealed
Ancient kings sealed important correspondence with a lump of wet clay, stamping the clay with a seal. These seals were often engraved in semi-precious stones such as brown carnelian. The seals of the kings of Judah featured handles similar to this one.
A dump site is the last place you would expect to find an 8th century B.C. seal for a papyrus document signed by one of the kings of Judah.