Eastcheap is an Illuminati submersible ship, filled with the Society's treasure. It is disguised to resemble an island. Falstaff and his gang of thieves were placed in charge of it after Falstaff joined the Illuminati. ("Strangled", "Losers")
Unless they were sold, its probable that the jewels Dominic Dracon and Mace Malone stole are currently stashed away on Eastcheap. 
Real World Background
Eastcheap is named after a district of London, which Shakespeare depicted as the favorite haunt of Falstaff and his friends in his Henry IV plays and Henry V. The Boar's Head Tavern, where they reveled and caroused, stood here.