Sha with breve (Ш̆ш̆) is an additional letter of the Cyrillic script which was used for Abkhaz and Komi at the start of the 20th century. It is composed of a sha⟨Ш⟩ with a breve.
Гулиа, Д. И.; Мачавариани, К. Д. (1892). Абхазская азбука (in Russian). Тифлис. GuliaMatchavariani1892.{{cite book}}: CS1 maint: location missing publisher (link)
Ч̆оч̆уа, А. М. (1909). АБХАЗСКАЯ АЗБУКА(PDF) (in Russian). Тифлис. Tchotchoua1909.{{cite book}}: CS1 maint: location missing publisher (link)