The Royal Mail Steamship Union presented the plaque on April 9, 1912, a day before the RMS Titanic began its fateful voyage from Southampton to New York, to the mayor and leader of the shipyard where the ship was built.
Inside the bronze and silver plaque, weighing 1.8kg and measuring 28cm by 37cm, was a small light that lit up an image of the ship on the outside.
"This, the Latest, Largest and Finest Steamer Afloat," the plaque reads.
However, 12 years ago a British man went to an art dealer in Barcelona, and tried to sell the relic because he "needed the money." He apparently did not know the relic's value.
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"The man brought the plaque to the Barcelona art merchant in a plastic bag and tried to sell it," president of the Spanish Titanic Foundation Jesus Ferreiro told The Local.
The art dealer bought the relic for his grandson who was a "Titanic fanatic".
Ferreiro said the foundation consulted with experts to confirm the authenticity and history of the plaque.