Ikom monoliths

From the longer Wikipedia page 
The Ikom monoliths are a series of volcanic-stone monoliths from the area of Ikom, Cross River State, Nigeria. Allison estimated that the monoliths may have been engraved between the sixteenth and twentieth century CE.
Numbering about 300 in total, the monoliths are between 0.3 and 1.8 metres (1 and 6 feet) high, and are laid out in some 30 circles located around Alok in the Ikom area of Cross River State. Since Cross River was divided, it now belongs to Akwa Ibom State. The monoliths are phallic in form and some feature stylized faces as well as decorative patterns and inscriptions. Although the carvings have not been deciphered, researchers and linguists believe that the inscriptions may represent a form of writing and visual communication.
The British Museum page is .
Category:Undeciphered inscriptions