Well, a visiting yacht/ship may fly their own state flag (if there is no national ensign) in Singapore waters.sundaymorningstaple wrote:The only exception I'm aware of is the flying of a nation's state flag on a registered diplomatic vehicle of that nation. Otherwise, I don't think it will fly....
Of course, they should also be flying the Red Ensign of Singapore too, as a courtesy flag. (Often see yachts with the Singapore flag on them, but that is also strictly prohibited - they should use the Red Ensign).