Father Catich wrote a book about Roman capital letters and how serifs that originated from brushwork by calligraphers painting the letters on stone, later chiseled-out by stone masons. The masons were always careful to follow the painted edges. This book he wrote, called The Origin of the Serif, was published over half a century ago.
During the Roman Republic, official notices were painted on walls by calligraphers, just like show cards were lettered for businesses in the late 19th and early 20th centuries in this country. In fact, Father Catich, in his youth, lettered show cards for a living before taking Holy Orders.
This stele found near the Dead Sea could be a piece that simply was never completed by stone masons after the ink was applied by a calligrapher.
That sounds like a very plausible theory.
Thank you for that information. That is very interesting, and likely.