I kinda doubt those were from South Arabian visitors. I remember a linguist friend pointing out to me that the "Berbers" of the north Somali coast living in those port-towns most likely did have a literate class. It would be a little odd if they did not given that they were making constant contact with Arabians, Indians, Romans, Greeks, Chinese... All people who had adopted writing at that point and also how during the Islamic period, when the same sort of trade continued, Reer Magaal Somalis wasted no time adopting Arabic as a written language, eventually even
creating a way to use it for Af-Soomaali.
And what's further intriguing about those inscriptions found all over the north is that they're often in the hinterland too. On grave markers, supposedly even under some cave paintings and just generally all over the place so unless Arabians heavily colonized the north which we have no archaeological, genetic or historical account evidence for; one wouldn't be far-fetched in assuming some of these inscriptions were probably made by locals. The wide spread of the inscriptions honestly brings Semitic inscriptions to mind:
In Arabia, contrary to popular Islamic belief, it seems there was a high literacy rate during the pre-islamic era to an extent not usually ever seen in pre-modern societies. They have inscriptions literally everywhere. On random rocks, boulders and so on and the messages seem like they were left by normal everyday people who left behind things like love letters, descriptions of everyday life, poetry or their names. Would be trippy if nomads in northern Somalia were once similar and literacy just dropped overtime during the Islamic era like in Arabia.
Plus, if you look at the small amount of ancient Yemeni in Somalis and run some proper models on it the stuff looks "Intra-Horn" mediated. As in from some sort of Oromo-Habesha type source rather than direct Arabian admixture like with Habeshas so I doubt it was left by ancient Yemenis our people traded with who clearly left no linguistic mark.
