The letter was a letter added to the Greek alphabet

Greek alphabet

The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

 in order to write the Bactrian language

Bactrian language

The Bactrian language is an extinct Eastern Iranian language which was spoken in the Central Asian region of Bactria. Linguistically, it is classified as belonging to the middle period of the East Iranian branch...

. It was similar in appearance to the Anglo-Saxon and Icelandic

Icelandic language

Icelandic is a North Germanic language, the main language of Iceland. Its closest relative is Faroese.Icelandic is an Indo-European language belonging to the North Germanic or Nordic branch of the Germanic languages. Historically, it was the westernmost of the Indo-European languages prior to the...

 letter thorn (þ)

Thorn (letter)

Thorn or þorn , is a letter in the Old English, Old Norse, and Icelandic alphabets, as well as some dialects of Middle English. It was also used in medieval Scandinavia, but was later replaced with the digraph th. The letter originated from the rune in the Elder Fuþark, called thorn in the...

, which is sometimes used to represent it in modern print, although both are historically quite unrelated. It probably represented a sound similar to English "sh" (ʃ). Its conventional transliteration in Latin is "š".
Its original name and position in the Bactrian alphabet, if it had any, are unknown. Some authors have called it "san", on the basis of the hypothesis that it was a survival or reintroduction of the archaic Greek letter San

San (letter)

San was an archaic letter of the Greek alphabet. Its shape was similar to modern M, or to a modern Greek Sigma turned sideways, and it was used as an alternative to Sigma to denote the sound . Unlike Sigma, whose position in the alphabet is between Rho and Tau, San appeared between Pi and Qoppa...

. It closely resembles, perhaps coincidentally, a letter of the Greek-based Carian alphabet which may have also stood for [ʃ]. The name "sho" was coined for the letter for purposes of modern computer encoding in 2002, on the basis of analogy with "rho" (ρ), the letter with which it seems to be graphically related. Ϸ was added to Unicode

Unicode

Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

in version 4.0 (2003), in an uppercase and lowercase character designed for modern typography.

Appearance	Code points	Name
	U+03F7	GREEK CAPITAL LETTER SHO
	U+03F8	GREEK SMALL LETTER SHO