This is a long and interesting article that is hard to excerpt. In brief: some recently discovered Arabic lapidary inscriptions at Bir Hima in Saudi Arabia, written in the old Nabataean (Nabatean) script, date themselves to c. 470 CE and mention a number of names. The iconography of the inscriptions is explicitly Christian. It is possible that the named people were martyrs, killed in a persecution by the Jewish Himyarite kingdom based in Yemen, a persecution we know of from other sources. This kingdom fell to Christian invaders from Aksum in Ethiopia in 500 CE. There was a Himyarite revolt in 522 led by a man named Joseph (Yusuf) and there is reference to him in another new inscription. A Yemenite Jewish community, arguably descended from the Himyarite kingdom, were transported to Israel in 1949-1950 in Operation Magic Carpet.
Now a few excerpts:
In 2014, researchers from a French-Saudi expedition studying rock inscriptions in southern Saudi Arabia announced they had discovered what could be the oldest texts written in the Arabic alphabet. But they did so very quietly, perhaps because the context of the texts is something of an embarrassment to some.The Jewish and Christian background to the rise of Islam is a cutting edge area of research that is being followed up, for example, by the Enoch Seminar. Some other recent relevant posts are here, here, here, and here.
The dozen or so engravings had been carved into the soft sandstone of the mountain passes around Bir Hima – a site about 100 kilometers north of the city of Najran, which over millennia has been plastered with thousands of inscriptions by passing travelers and officials. Conveniently, at least two of the early Arabic petroglyphs that were discovered cited dates in an ancient calendar, and expert epigraphists quickly calculated that the oldest one corresponded to the year 469 or 470 CE.
The discovery was sensational: the earliest ancient inscriptions using this pre-Islamic stage of Arabic script had been dated at least half a century later, and had all been found in Syria, which had suggested that the alphabet used to write the Koran had been developed far from the birthplace of Islam and its prophet.
According to the report, the Arabic text, scrawled on a large rectangular stone, is simply of a name, “Thawban (son of) Malik,” followed by the date.
Underwhelming? Well, there is the matter of the large, unmistakably Christian cross that decorates the head of this inscription. The same cross systematically appears on the other similar stelae dating more or less to the same period.
According to Christian chroniclers, around 470 (the date of the Thawban inscription), the Christians of the nearby city of Najran suffered a wave of persecution by the Himyarites. The French experts suspect that Thawban and his fellow Christians may have been martyred. The choice of the early Arabic script to commemorate them would have been, in itself, a powerful symbol of defiance.
This pre-Islamic alphabet is also called Nabatean Arabic, because it evolved from the script used by the Nabateans, the once-powerful nation that built Petra and dominated the trade routes in the southern Levant and northern Arabia before being annexed by the Romans in the early 2nd century. Used at the gates of Yemen, this northern alphabet would have stood in sharp contrast to the inscriptions left by Himyarite rulers in their native Sabaean.
“The adoption of a new writing signaled a distancing from Himyar and a reconciliation with the rest of the Arabs,” the French researchers write in their report. “The inscriptions of Hima reveal a strong movement of cultural unification of the Arabs, from the Euphrates to Najran, which manifested itself by the use of the same writing.”
There's more on the Nabataean script (ancestral to the Qur'anic Arabic script) here. More on the Himyarite kingdom and its conflict with Axum is here. There are many past posts on the ancient kingdom of Axum and the city's more recent history. See here, here, here, here, and links. The kingdom of Sheba and the legendary Queen of Sheba are also mentioned in the article. See some of those posts just cited in the last sentence, as well as here and links for background.