The Origin & Evolution of Ancient Arabian Scripts – by Dr Majeed Khan.
This is a link to another ‘downloadable book’ on the subject of rock art research: this time with emphasis on Proto – Arabic script.
He puts forward the idea that rock art was a precursor of Arabic script, considered a somewhat polemic conclusion by some: but if the Arab Bedouin used rock art as an eventual form of communication, then it is not unreasonable to conclude that it could develop into a proto – Arabic script.
If you do not have a Facebook account (I certainly don’t – Life style!) it can still be read on line.