This is a well known flag. Banten is a city in the north of Java, and was a Dutch factory in the XVII century. It was capital of a native sultanate, and later was annexed by the Dutch. Its importance decreased in favour of Batavia. The flag is probably that of the Sultan. Yellow is frequently a symbol
of royalty in this area (e.g., Brunei and some Malay states). This image, with minor variations, is known from several old plates. The version shown here is from a Japanese plate from 1876. Jaume Ollé, 17 January 2000
The name was used as Bantam by the Dutch
at the time the city flourished, but its native name was Banten. According to
the Encyclopędia Britannica the estuary silted up and the city became a ruin. Mike Oettle, 15 March 2007