What was the paper Ace gave Luffy?

Ace gave Luffy a piece of his Vivre Card. In their meeting Luffy receives the item from Ace who states that the paper will bring them together in the future. ch. 159, p. 12 Luffy initially reacts with confusion calling it a scrap piece of paper. ch. 159, p. 12 Later the item is recognized as a Vivre Card that displays the life force of the holder and fades when the person is in danger. ch. 489, p. 16 Nami confirms it matches the white paper Luffy received from Ace. ch. 489, p. 16 Yamato later returns another portion of the same Vivre Card to Luffy explaining its purpose for future meetings. ch. 1000, p. 5 "Yes, and that piece of paper will bring us together in the future." ch. 159, p. 12 "THIS PAPER WILL LET US MEET AGAIN." ch. 489, p. 16 "YOUR VIVRE CARD!" ch. 1000, p. 5