A sign similar to Figure 1 has become increasingly common in recent years; many, including the author, carry this ancient Christian symbol on their cars. Probably few know that it is a simple mathematical curve. It is of course questionable whether Apollonius knew it, though he could have done, and even more questionable that early Christians knew their Apollonius. But they certainly knew some form of the symbol. Nowadays it is often crudely reduced to two circular arcs - making steering difficult for the poor fish.