The British Trade Dollar was a form of bullion coinage issued by the United Kingdom and intended to facilitate foreign trade in East Asia.
The years between 1875 and 1895 saw a rapid fall in the price of silver, which apart from disrupting trade also resulted in a serious shortage of minted dollars. To overcome this shortage, approval was given in 1894 for the minting of these British Trade Dollars, for general use in the Far East.
The coins were designed by designed by George William de Saulles and depict on their obverse a the figure of Britannia standing on shore, holding a trident in one hand and balancing a British shield in the other, with a merchant ship under full sail in the background; this is instead of the British monarch as would normally be the case on British coinage, in order to make them acceptable outside the British Empire. On the reverse is an arabesque design with the Chinese symbol for longevity in the centre, and the denomination in two languages - Chinese and Jawi Malay.
In 1895, the British Trade Dollar was given legal status in the British colonies of Straits Settlements, Hong Kong and Labuan. Its circulation in the Straits Settlements and Labuan was of short duration; after the Straits Settlements introduced their own Straits Dollar in 1903, the British Trade dollar was demonetised there in 1904 and 1905 respectively. It became exclusively a Hong Kong coin produced until 1935. Thus, it was known as a Hong Kong Dollar for most of its existence, and was only legal tender in that colony for most of the time.
Note that many of the genuine dollars are found with "chop marks" - small Chinese ideographic marks punched by local banks and counting houses to signify a coin was checked by them. The practice was prohibited in Hong Kong and eventually fell into disuse. These marks are considered to not detract from the value of the coin; on the contrary - many collectors appreciate them as a piece of history.
The British Trade Dollar was finally demonetised in Hong Kong on 1 August 1937.