Auxiliary handstamp, POSTAGE DUE
If a First Class mail piece had at least the base postage for the first ounce, but did not have the full postage due, a postal clerk stamped the mail "POSTAGE DUE ____ CENTS" and manually filled in the difference in postage. The notation was applied at the delivery office and the carrier or window clerk collected the shortage from the mail recipient. These handstamps were introduced when the postage due adhesive stamps were discontinued.