The wild goose.
Legend has it that a Chinese ambassador was mistreated by a treacherous prince.
The ambassador wrote letters describing his condition and attached them under the wings of wild geese. One of the migrating geese was brought down by the Emperor while hunting, who found and read the letter. He freed the ambassador and punished the prince for daring to mistreat his representative. When a post office clerk sold a stamp across the counter to a patron, he would cut or tear it before it was placed on the letter. This was a sure preventative against reuse, for the stamp could never be accepted for postage prepayment again.