Marked with an official signature or sign that allowed mail to be sent free of charge; also, to privilege or authorize.
Past tense of frank, from Old French franc meaning 'free.' In postal history, franking was when officials marked mail with their signature to indicate it could bypass postal fees, a privilege of members of parliament and nobility.
Benjamin Franklin famously used his postal privileges to send franked mail, and there was so much political mail abuse of the franking privilege that it nearly bankrupted the postal service in the 1800s—essentially politicians were running free mass mailing campaigns on taxpayer money.
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