Flag of St David

The flag of Saint David (Welsh: Baner Dewi Sant) is normally a yellow cross on a black field, but it has also appeared as a black cross on a yellow field or with an engrailed cross. It represents the 6th century Saint David (Welsh: Dewi Sant; c. 500 – c. 589), a Welsh bishop of Menevia and the patron saint of Wales.

The Flag of Saint David has been used as a flag representing Wales (as an alternative to the Red Dragon flag), in the same sense that the crosses of Saint George, Saint Andrew, Saint Patrick and Saint Piran are used to represent England, Scotland, Ireland and Cornwall (of which they are respectively patron saints). It is similar to the arms of the Diocese of St David's.

The flag can be seen throughout Wales, but not as frequently as the Red Dragon. On Saint David's Day it often plays a central role in the celebrations.

The flag of Saint David was mostly unknown in Wales until 1994. There was a large one along the roof in St David's Cathedral with the cinquefoils thereon but hardly any others in use. The Welsh Tartan Company (WTC) were looking around for a 'brand' to complete the Brithwe Dewi Sant (St David's Tartan)/J Wake, then of the WTC, set out to see if the flag could be used commercially or indeed patriotically across Wales. The feeling at the time was that the Union flag did not contain any Welshness, the St George's Cross representing Wales as a principality of England. The Dean of St David's said that the cinquefoil and the cross were their property and advised help from a London royal official office.

...
Wikipedia