I learned that Ajami is a modified Arabic script that fused with local languages, especially in parts of Africa.  The article mentioned that followers of Muhammed traveled to Ethiopia following early persecution in the Arabian Peninsula.  This meant that parts of Africa came to have followers of Islam prior to parts of the Arabian Peninsula.  From what I've read, Ajami uses extra dots, lines and other markings to make sounds that are not usually found in Arabic, but blend Arabic with local languages.  

Here was one source of information that I found: https://guides.library.yale.edu/c.php?g=1530945&p=11469515

This other source (video) talks about how all kinds of communication, including poetry was written in Ajami.

Source: https://www.google.com/search?q=what+is+ajami&rlz=1C5FPAB_enUS1221US1221&oq=what+is+ajami&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIHCAEQABiABDIHCAIQABiABDIICAMQABgWGB4yCAgEEAAYFhgeMggIBRAAGBYYHjIICAYQABgWGB4yCAgHEAAYFhgeMggICBAAGBYYHjIICAkQABgWGB7SAQgyMzY2ajBqN6gCALACAA&sourceid=chrome&source=chrome.ob&ie=UTF-8&safe=active&ssui=on#fpstate=ive&vld=cid:ea6cac99,vid:Of_3TGDiQPQ,st:0