The Portland Observatory was built in 1807 by Captain Lemuel Moody (1768-1845), a sea captain who saw the possibilities and advantages of making a living from the sea while staying on dry land.
Although appearing to be a lighthouse, the octagonal, 86ft tower erected on a peninsula known as Munjoy Hill was used to alert merchants and ship owners that their vessels were approaching.
Moody devised a system of "signalizing" the arrival of ships by flying a particular combination of signal flags from the top of the observatory.
A jug like this is discussed and illustrated in Success to America: Creamware for the American Market where it is suggested that Moody may have personally ordered 75 of these 9in (22cm) high jugs in Liverpool or Staffordshire c.1807 to give or sell to subscribers to his service.
They depict a view of the observatory and a key to his 24-flag system while to the reverse is a ship flying the American flag.
The authors speculate that they were probably meant to be inscribed with the name of a vessel, in this case the Washington.
Only a handful of these jugs are known and closer to the top of the market examples have brought as much as $20,000. However, this example which was offered on August 18 was allowed to sell below hopes of $5000-8000.