The only flag with a trident on it
Barbados, and nothing else in the atlas. The sentence under it is where that is written down.
- Barbados
A black trident head, commonly called the broken trident, is centred in the golden band, and the fact that the staff is missing is significant.
Flag of Barbados on Wikipedia
How a flag gets onto this list
A flag is here because its own English Wikipedia article says so, in the sentence printed under it. Nothing was decided by looking at the picture: colours can be measured off a drawing and a lion cannot, so this list defers to a source anybody can check rather than to our opinion of what we are seeing.
That also means the list is short rather than wrong. Where an article never gets round to describing what is on the flag, that flag is missing from these lists even though the symbol is plainly there — and we would rather be caught missing one than caught inventing one.