The crowned C
In was usual in olden days numismatics, and even nowdays in some cases, that coins held symbols regarding the place/city where they were strucked.
In this sense in Spanish numismatics, the crowned M, was the symbol of Madrid since about 1728.
But during the Napoleonic wars, what we call the War of Independende (1808-1814), most of Spanish mainland cities were ocupied by the French troops with the exeption of Cadiz, were in absence of the true King FERDINAND VII, kidnapped in France by Napoleon, the "true government of the Spanish nation and overseas territories was in CADIZ.
Thats the reasson why in those years, Cádiz´s mintmark stopped being a C to become a CROWNED C, as you can observe in the following piece.
8 REALES (Spain - Cádiz - 1813 - 27,07g - 903 SILVER - 42mm)