When brought to King Roald, the player would complete the quest and receive 600 coins as a reward. If you choose to destroy the complete certificate, you had to go back to your respective gang and get another shield half part.
The certificate was written by the curator of the Varrock Museum to verify that the player had returned the Shield of Arrav to the museum of Varrock. The reward was in accordance with the proclamation laid down by King Roald II in the Year 143 of the Fifth Age, when the shield was stolen by the Black Arm Gang.
The bearer of this certificate has brought both halves of the legendary Shield of Arrav to me, Haig Halen, Curator of the Varrock Museum. I have examined the shield and am satisfied as to its authenticity. I recommend to his majesty, King Roald III, that the bearer is rewarded as per Proclimation 252 of the year 143 in the 5th age, by King Roald II.