Provincia de Sierra Madre (Philippines)

In my TL "Filipinas: La Gloriosa y Más Allá", a new Chavacano-speaking province was created through a plebiscite, which was said by some as compensation for the unification of the Tagalog-speaking provinces into a single entity, the province of Kumintang, because they were celebrated in the same month. It was named Sierra Madre, after the mountain chain, and its capital was the town of Montalbán.

For creating this flag, I've saved the flag of Slavonia from Wikipedia, then edited on MS Paint; first, I've inverted the flag (from blue-white to white-blue), then draw a triangle using the red line, filling it later. Then, I've copied one of the flags of the Katipuneros, and pasted the sun from the said file.