The scallop shell is the symbol of the Camino. It is on every sign along the way. I’ve read that there are historical or mythical connections (depending on your point of view) between the shell and Saint James. I also read that the shell symbolizes the different Camino routes converging in the same place.
To me, it’s also a symbol of the way you feel connected to all the other pilgrims – the ones you meet, the ones you pass and the ones who walked the path a thousand years ago.