U is for Universal Postal Union

Universal Postal Union
Universal Postal Union Cinderella Stamp

The Universal Postal Union {UPU} is an international organization of postal administrations, established in 1874 to regulate mail between countries. Today, almost 200 countries belong to the UPU, which continually revises standards and procedures for international rates, accounting, reimbursement,and other complexities of global postal operations.

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2¢ + 2¢ postal reply card

The purchaser of this card bought four cents worth of postage, 2¢ to deliver it overseas and 2¢ to pre-pay the "return trip." A reply card is acutally two attached cards; by separating the unused portion, the recipient can answer without affixing postage. United States, 1893.