I moved to South Florida some months ago and recently bought a home which will be in renovations until September. I will be working as a volunteer at the Pilgrim Office from late- July to late August this year. My plan is to obtain a suitable scallop shell emblem in brass or other weather-resistant media to bring home to affix in my rear garden - likely inside the screened-in lanai outdoor room.
In any event, I plan to point the hinged side of the scallop in the direction of Santiago. That would be pointing due East, towards Santiago from where my "new" home lies. I am in the "all routes converge at Santiago" camp.
On different Camino routes, or in different regions or provinces, you will see the scallop shape pointed in many different directions. however, and IMHO the only logical placement, given the millennia long, and more, practice, all the various pilgrimage paths were always intended to converge and end at the tomb of the Saint at the Cathedral in Santiago. Hence, IMHO the hinge side should be placed in the direction of Santiago de Compostela.
However, if you are placing the shell vertically, over a doorway for example, you can make a logical case to place the hinge side up or down. It depends on perspective. If you believe that all routes lead UP to Santiago, you might place the hinge side UP. On the other hand, if you interpreted the issue as all Camino routes flowing like water, to Santiago, then you could made a logical case for placing the hinge side DOWN, as water always flows with gravity.
My "new" home has a screened-in vestibule in front of the main, front door, over the lower doorway, there is a large screened panel in the shape of a scallop. The real estate folks call it a "sunburst." But as a four-time pilgrim, to me it is a concha. Anyway, this one has the "hinge" side DOWN. My non-pilgrim wife immediately recognized it as a Camino shell as soon as we drove up to view the home the first time. Perhaps it WAS Santiago who influenced our immediate and strong preference for this home...
As an aside, I am considering figuring out how to manufacture dense foam or resin versions of the distance marker "mojones" found along the Camino routes. Each would have the glazed, ceramic scallop shell, an arrow, and a noted exact number of kilometers to that center spot in the Plaza de Obradoiro in Santiago in front of the Cathedral. Stone would be ideal, but far too expensive to ship. I would love one for my home and I am willing to think many other Camino folks would also want one. Anyway, I am noodling this one over in my mind. In April, I took precise measurement of the newer style of mojone being installed across Galicia. Still thinkin...
I hope this helps...