Ichthys

AKA the Jesus fish. referred to as such Because early in the century, the Roman Empire was actively seeking  Christians for persecution and death. Often people were hesitant to to reveal their faith to strangers for safety sake so in order to determine if a stranger was also a Christian the Christain would Draw and arc in the sand and if the other person drew an opposing arc(completing the shape of a fish) then they were indeed a Christain. Though the roman empire fell and certainly the vehicles and means of communication has Improved Christians all over the world suffer persecution, torture and death. And now it is not a symbol of safety...but of solidarity and faith.