Khatt ar-raml or "sand writing" an Islamic form of geomancy. Not just found in African but the use is strong in Islamic Africa.
While trying to find info on something altogether different. I started to read an essay by Louis Brenner in a Smithsonian Institute Publication- Insight and Artistry in African Divination, available from amazon. This system of divination is a series or pattern of dots thought to originate from stones thrown on to sand. Details of the actual and varied styles of systems used is not fully researched.
Dot patterns are seen on many Saharan blades and other Islamic weapons. These patterns are often shown in very schematic ways. Making me think there could well be more to these than meets the eye.
I cannot type out pages of this book but I will add just a glimpse of the hypothesis. I cannot see any reason why some system of dots are not put down in a talismanic way. Just remember Morse code. This would also have all that magic benifit to it as well.
