Columbus' signature was a combination of Byzantine-Greek and Latin. He signed his name Xpo-Ferens, the first part being Greek and the second Latin. He wished his heirs to continue to "sign with my signature, which I now employ, which is an X ["CHI"] with an S over it, and an M with an A over it, and over that an S, and then a Greek Y with an S over it, preserving the relation of the lines and points." (Morison p.202.). Columbus added his title "Admiral" to his signature later in life.
Nobody has been able to decipher Columbus' strange signature. The last line reads: Chrispto Ferens, "Porter of Christ' , the rest can be interpreted as anything you want to read into it. People have used the signature to "prove" that he was Greek, Portuguese, Jewish...