Looking the same, but sitting on the base line. Must be distinguished from u,v,y. The same enlarged. Occurs only after certain consonants. Y with curl on the right diagonal.
Many african languages are tonal languages like chinese.
Usually, tones are marked by acute, grave and circumflex. Efik also uses the prime accent and the hachek. My opinion is not to include such combinations as seperate letters into a standard. A text processor should be able to ceate them by using floating diacritics. This point is hard to evaluate.