The term "Aroko" in Yoruba describes the system of communication using objects, such as cowry shells, feathers, or Palm fronds, each object having a certain meaning depending on how it was placed or combined on the ground.
There are characters that represent the seven Yoruba vowels, as well as each consonant/vowel combinations for each of these seven. Gba, gbe, gbi, gbo, ka, ke, ki, ko, etc.