Hi, Phil , an import and duty mark Kingdom of Belgium, used 1 March 1832 till first January 1869. The mark a gothic E in a double ringed round shield. E= étranger=foreign. This mark does not give any guarantee of a precious metal standard of fineness. Used on metal with 250 minimum gold or silver content as a duty mark. The mark was destined for all imported, unmarked and invalid marked objects of foreign, national and unknown origin.
See:
viewtopic.php?f=24&t=46656&p=138142&hilit=Gothic+E+oel#p138142Peter.