I think it is as simple as saying "Christ crucified". If someone doesn't understand, or mocks the Christian who says this we know. If a church does not believe this is sufficient (adding to The Gospel) we know they are not with us.
AMEN!
It really IS that simple. And as has been said, we can disagree on many things... and goodness knows there's enough of those things. But the basic tenants of faith are the same: Christ and Him crucified. Faith alone; Christ alone.
Hoss