The Stone of Golorr was initially introduced to D&D fans as an object of power hidden on Earth by Elminster, a famous wizard in Forgotten Realms lore. The tagline "Leave no Stone Unturned" was included in morse code at the bottom the announcements for WotC's Stream of Many Eyes (SoME) production, and was the first reference to it. Soon after, WotC invited fans to play an online treasure hunt for the Stone through an alternate reality game (ARG), where they had to solve multiple puzzles (including symbols, musical notes, and calculations, some of which were flashed on the screen during D&D streams or on the Twitter accounts of the players--including DCA). Fans would then decipher the clues to reveal the name of the person currently holding the Stone (whose mind was wiped to protect them) and the 'spells' that would restore their memory and send them back to the Forgotten Realms.
"The Sage of Shadowdale hath hid on Earth a stone, of power great and imminent import. Its guardian, an exile from my realm, was spirited to Earth with this in tow; To keep it safe and secret 'ere its prophesied return."
"The hour of its need now soon at hand, this item and its wielder must be found; Sent, via portal, back from whence they came. At long last, well and truly homeward-bound."
The guardian was revealed to be Volo, while Halaster Blackcloak--who is responsible for the setting of the future module Waterdeep: Dungeon of the Mad Mage--admitted to being one of those seeking the Stone for his own selfish ends. In the ARG, fans were meant to choose where the teleportation spell would take Volo, but WotC ultimately made him appear in Waterdeep at the 'SoME' event for the live games being played there. During an 'off the table' show between the streams, the players learned that Volo had the Stone stolen from him, and they had to solve more puzzles to recover it. Mark Hulmes's character then snuck onto the "Dark and Dicey" stage and handed the Stone to their team, who have had to deal with the talkative, sentient artifact ever since (which they renamed the Google MacGuffin).
The Stone in DCA Edit
Jared, Holly and Anna were each mailed USB keys shaped like actual keys, which had picture files of symbols to show fans on their Twitter accounts to help solve the puzzle. Similarly, at the end of Ep 93, Chris told Diath, "You hear a strange humming...you track it to your key ring." Chris then explained that Diath now has an extra ring with "a strange symbol on part of it. It's a silvery key, and the symbol looks like a crescent moon, lying bowl-shaped with a dot above it". The key has not been referred to on the show since, however, right afterwards, Chris described the symbol on the key mailed to Jared, implying that Diath's key might also be tied to Elminster in some way. During the 'off the table' show, which is supposedly canon between the streams at SoME, Elminster was shown as being in Waterdeep.
During episode 95 at the SoME, Dani Hartel (playing her character Wandala) began telling the Crew about the Zhentarim's plans, saying, "The Xanathar and us, and I assume a lot of other people, are looking for the Stone of-" before Chris quickly cut her off. The other streams the next day at SomE explained that the Masked Lords of Waterdeep sent agents to find the Stone, and that it was tied to finding the location of a secret hoard of 500,000 gold coins (named 'dragons', which is the topic of the upcoming module "Waterdeep: Dragon Heist"). In episode 96 of DCA, also taking place at SoME, the Crew were tasked with protecting Renaer Neverember from the Xanathar, who wanted the location of the Stone. Renaer's father supposedly created it to store the knowledge of the location of the treasure hoard, before he was banished from the city. Renaer denied knowing anything about it, except that its magic caused you to forget anything you had learned once you put it down. A Zhentarim assassin also tried to attack them, but was captured by the Crew and revealed to them the connection between the Stone and the hoard. Representatives from the 7 dwarf clans of the North then confronted Diath over his release of the fire primordial in Ironslag, and revealed that their seers foresaw Diath coming into possession of the hoard. The dwarves demanded that Diath agree to give them the treasure as payment, especially since the gold had been "taken from dwarven mines".
When Lady Esvele Rosznar visited the Crew, she revealed that she had come into possession of the Stone, and was seeking three key items to help open the vault of the treasure (Drow assassins sent by Jarlaxle then attacked them, and luckily one of their hands provided a needed key item. A tentacle Strix had cut off a slain beholder provided another, and Esvele convinced the Crew to help her infiltrate the Morgaster estate, where she stole a jeweled necklace that was the third). The Cassalanters then told the Crew that Esvele was planning to auction the Stone to the highest bidder.
 Elminster. Wikipedia
 http://dnd.wizards.com/articles/events/some. Dungeons & Dragons website.
 Volothamp Geddarm. Wikipedia.
 Halaster Blackcloak. Forgotten Realms Wikia.
 The Stream of Many Eyes: Day 2. PowerScore RPG's blog.