Do Christians have "secret" (handshakes for example) ways of knowing who other Christians were? Did Christians ever come up with "secret" ways of knowing who other Christians were? I don't mean exactly a handshake, because I get that sometimes people don't (or can't) shake hands. Seems like it might be a bit pointless, like a joke you have with friends or something. But did they?
The Sator square was likely used to secretly advertise a house as Christian to other Christians in the first century.