The symbol of the Pilgrim to Santiago is the Scallop shell of which many can be found on the coast of Galicia and it is actually a symbol of the Pilgrimage (and has become a symbol of other Christian Pilgrimages too) partly because you could find the shell easily there and so could go back home and show it off as proof that you had done the Pilgrimage. It has also been included in carvings in some Churches. S callops also serve a practical purpose for medieval pilgrims as it is the correct size for getting water to drink or to use as a small bowl to eat their food from.
A blog about the Pilgrimage to Santiago de Compostela