That taboo already existed even before the New Testament was written. The Septuagint, an early Greek translation of the Old Testament, was written around 260 BC and uses this convention, translating the Lord's name as "kyrios"- "Lord." The authors of the New Testament itself extensively quote this translation, and firmly established this convention within Christianity as well, especially because most Christian converts wouldn't know Hebrew or be expected to learn Hebrew to hear (remember that literacy rates were very low in this era compared to now) Jewish scriptures in their own languages.
Speaking of literacy, I notice that the Latin of this inscription is very messy. I don't know much Latin myself, but the handwriting is terrible, to the point where I wonder if the maker of this scroll was only semi-literate.