Liechtenstein and Haiti had the exact same flag. They found out when they competed in the Olympics!
A country’s flag is a symbol of pride and unity. It is waved proudly at special events and shown special respect. It makes sense then that a flag should be unique and easily identifiable.
However, countries also often try to keep their flag designs simple, and this can lead to problems. This was the case with Liechtenstein and Haiti. Both countries had a flag that consisted of a horizontal blue stripe on top of a horizontal red stripe. Pretty straightforward.
They didn’t realize this until they competed against each other in the 1936 Summer Olympics. Awkward. In order to remedy the problem, Liechtenstein added a gold ducal crown on the hoist side of the blue stripe on their flag. Now they won’t be mistaken for Haiti.