When I designed the fc fonts for use with TeX I researched character usage by African languages and found at least one language using a capital esh. I saw good quality specimens in printed matter and the capital Esh is in some sense smaller than its lowercase conterpart, it has the height of a normal capital letter and no descender. It was integral shaped. I did not find evidence for contemporary use of a Sigma-shaped capital Esh then (early 1990ies), but is was used historically in now obsolete orthographies.
The full list of languages I inspected is: Akan, Bamileke, Basa (Kru), Bemba, Ciokwe, Dinka, Dholuo (Luo), Efik, Ewe-Fon, Fulani (Fulful), Gã, Gbaya, Hausa, Ịgbọ, Kanuri, Kikuyu, Kikongo, Kpelle, Krio, Luba, Mandekan (Bambara), Mende, More, Ngala, Nyanja, Oromo, Rundi, Kinya Rwanda, Sango, Serer, Shona, Somali, Songhai, Sotho (two different writing systems), Suaheli, Tiv, Yao, Yoruba, Xhosa, and Zulu.
I can now confirm that it was Gã, I have found my old notes again.