Was the Khotanese Brāhmī subscript hook borrowed from the Kharoṣṭhī anusvāra?

The sign inventory of the Brāhmī script used to write down Khotanese, an eastern Middle Iranian language once spoken in the southwest of the Tarim Basin, includes three additional diacritics. These are the two dots over an akṣara, the St. Andrew’s cross, and the subscript hook. The first two diacritics have already been detected in several Kharoṣṭhī documents from the Khotan area. In Khotanese, they represent respectively [ә] and [aә]. The subscript hook, on the other hand, seems to be restricted to Khotanese Brāhmī, but its specific linguistic function, palaeographical developments, and ultimate origin are still a matter of debate among scholars. This article offers a critical overview of the relevant scientific literature and introduces the results of a preliminary palaeographical analysis of the diacritic. The analysis shows that the subscript hook used in Khotanese Brāhmī was borrowed from the Kharoṣṭhī anusvāra. The proposed borrowing trajectory sheds light on the linguistic function of the diacritic as well.