In explaining why John’s gospel presents Thomas calling Jesus “my Lord and my God” in John 20.28, the scholar Adela Yarbro Collins interprets it within a context in which Roman emperors were given titles such as Lord, Son of God, God, and Saviour, and the combined title “Lord and God” in particular. By applying all those titles to Jesus, the author of the gospel of John was asserting that Jesus is equal and surpasses any of the claims that could be made for Caesar. Couldn’t this inscription be saying something similar? The gospel of John, in common with the rest of the NT, also clearly shows that Jesus is distinguished from God and is subordinate to him - John 14.28, 17.3, 20.17, and many other passages. Being greater than Caesar clearly does not necessitate being the one true God.
Whatever the phrase does mean, its meaning needs to be found in its own setting, not in future understanding about the Trinity that hadn’t even been developed yet. Say we found an early modern text that used the phrase “moon landing”. It might be a perplexing phrase, but whatever its real meaning is, it needs to be sought and found in the early modern context, not 1969.