Below is a section of a mosaic floor of what is probably the earliest Christian church accidentally discovered in Israel in the late '90s.
The mosaic is dated at around 230 AD, or about 200 years after the Christ's crucifixion, death, resurrection and return to heaven.
The inscription is in Greek, and reads:
“The God-loving Akeptous has offered the table
The table referred to was likely donated to the church by a woman called Akeptous.
"The words “God Jesus Christ” on the next-to-last line are abbreviated in the form of a contraction consisting of the first and last letters of the two words. Above the two sacred words is a straight line. While these abbreviations and the line above indicating sacred words was later a common practice, this is their earliest attestation. And this is the earliest inscription ever found in Israel, and perhaps anywhere, that mentions Jesus Christ!" -- from Biblical Archaeology Review
The phrase "God Jesus Christ" is the same phrase used by early Church Father, Ignatius (ca. 30-107 A.D), bishop of Antioch.