It all depends on what you are having authenticated. The authentication of signatures are based on past examples of a player's hand writing. A game-used bat will be authenticated by identifying characteristics attributed to a player and team records of bats that were ordered for that player. Authentication is verifying the originality or genuineness of an item.
Authentication can be based on provenance, which is the history of ownership of a particular item. It allows the buyer to secure additional insight as to the origin or chain of custody of the item.
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