Hi, Eric —
Thanks for the question.
- I am a graphic designer and am curious about when exactly the "cross" came about in addition to who chose it and why it was chosen to be the [logo|symbol] of Christianity?
The web page Mary Ann referred you to can answer questions referring to the history of Crucifixion.
The Church chose the Cross and the Crucifix (the Crucifix being the Cross with the corpus of Jesus on it) to be the logo or symbol of Catholic Christianity for obvious reasons.
571 The Paschal mystery of Christ's cross and Resurrection stands at the center of the Good News that the Apostles, and the Church following them, are to proclaim to the world. God's saving plan was accomplished "once for all" by the redemptive death of his Son Jesus Christ [on the Cross].
- I also heard that some biblical scholars think that it wasn't literally a cross, as we know it, but could have possibly been an X?
Ignore them; these type of Biblical scholars just scandalize the Christian faith. What my colleague Mary Ann referred to is what the Jehovah Witnesses falsely claim, that Jesus was crucified on a beam or post. The October 1991 edition of This Rock Magazine has an article written by a good friend of mine who passed away recently, Clayton Bower Jr.
They have no historical evidence for their claim.