Saint Barthélemy has no official flag. What gets flown in its place is the island's coat of arms, and the arms record an unusual detour: for nearly a century this French Caribbean island belonged to Sweden.
Handed to Sweden, sold back
France claimed Saint Barthélemy in 1648. The Knights of Malta held it briefly, from 1651 to 1656, in the course of the Order's short career as a Caribbean landowner. In 1784 it went to Sweden in exchange for trading rights in Gothenburg. Swedish rule reshaped the island's administration and its symbols, though the population remained largely French in origin and custom. In 1878 the island returned to French administration, and French symbols and practice came back with it. From 1946 it was a commune of the department of Guadeloupe, and in 2007, after a referendum, it became an overseas collectivity in its own right with considerably more autonomy.
The arms in place of a flag
Two pelicans stand on either side of a shield divided into three horizontal bands, and each band records one of the island's owners. The top band, blue with three gold fleurs-de-lis, is for France. The middle band, red with a white Maltese cross, is for the Order of Malta. The bottom band, blue with three gold crowns, is for Sweden. A gold mural crown sits above the shield for civic authority, the pelicans stand for the island's wildlife, and a scroll beneath carries the word Ouanalao, the name the island's indigenous inhabitants gave it.
The result reads as a layered receipt rather than a design: three rulers stacked in order of arrival, with the pre-colonial name underneath all of them. The arms are recent, though the history in them is not. Saint Barthélemy had none until 1977, when a French directive prompting municipalities to adopt civic emblems sent the island to the heraldist Mireille Louis, who drew the design it has used ever since.
Where it appears
With no official flag to fly, the arms do the work. They appear on government documents, websites, and local insignia, and on flags at civic and ceremonial occasions, usually alongside the French tricolore. Protocol governs those displays. Local festivals sometimes adapt the imagery to emphasize one element or another, and it turns up at Carnival and on Bastille Day.
Other French territories
Using heraldry as a de facto flag is common across France's overseas territories. Mayotte does the same thing, flying its departmental arms on a white field with no legal standing behind them. The pattern is easy to read: a French element to mark the tie to Paris, local imagery for everything else. Martinique is the exception that shows what the alternative looks like, having voted itself an actual flag in 2023.
References
Official site of the Collectivity of Saint Barthélemy
French Government's Documentation on Overseas Territories
"Vexillological Studies," FLAGS magazine, 2023.
"Caribbean Colonial History Archives," University Press.