The scallop is in reference to both the Camino de Santiago as well as St. James himself, for whom the aforementioned pilgrimage is named. The scallop has been symbolically associated with the Camino de Santiago since the medieval era, and possibly much earlier given the route’s origins as a Celtic path to the end of the world. Long before it was a symbol for St. James, the scallop was said to be a symbol of the setting sun.
The colorful career of St. James ranged from fisherman to apostle to martyr to a posthumous role of mythical Moor-slayer, roles which I will elaborate on at some point.
St. James is also the patron saint of Spain.