Belgian Hop Seal, Image & Found by Derfel.
"off the Thames foreshore, 14.7g 20mm."
One side has an annular border formed by two continuous dotted circles. In the centre is HOUBLON above DALOST above 1873. Within the annulus is the inscription BELGIQUE at the top and below FLADRE ORIENTAL*. The other side has a crowned shield bearing an sword pointing upward with a further small shield either side of the blade.
Houblon is French for Hop and this seal was found on the Thames foreshore at the nearest riverside bridge and wharf to the Hop Exchange.
Coat of arms of Aalst (a double headed eagle and a lion rampant each on separate shields either side of a sword pointing upright) - "Alost is the French name of the city and was used in the 19th century" identified by Knorrepoes on the Flags Forum.
From Wikipedia:- "Aalst (French: Alost) is a city and municipality on the Dender River, 19 miles northwest from Brussels. It is located in the Flemish province of East Flanders. The municipality comprises the city of Aalst itself and the villages of Baardegem, Erembodegem, Gijzegem, Herdersem, Hofstade, Meldert, Moorsel, and Nieuwerkerken-Aalst. The more rural regions are noted for their production of hops, which are sold to the old breweries there."
*Information from Rinus Van Nieuwenborgh:- "I notice that your bag seal text underneath “Belgique” is unclear: it says “FLANDRE ORIENTALE”, which means “East Flanders” in French, which is a province in the Flemish region of Belgium. Wikipedia."