Statement of authenticity
A letter of authenticity was a document that assured that an object was the genuine article it claimed to be.

A statement of authenticity was a certification that an item was the genuine article, not a forgery or counterfeit.

In 2369, Quark promised  that each Gamma Quadrant artifact he was selling came with a statement of authenticity from Vash, who the Ferengi described as "the Federation's foremost expert on the Gamma Quadrant" ()

In 2370, Odo questioned whether there was supposed to be a letter of authenticity on Plegg's vacuum-desiccated disks. Quark pointed him to the Ferengi Seal of Dismemberment. ()

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