这个音归属于“非标准”国际音标一类。

ɿ reversed fishhook R / turned iota,  it's a high back unrounded vowel, with frication from the preceding consonant, used by Sinologists, and by Japanologists studying the phonology of the Miyako language.

ɿ 形状上象倒鱼钩R，或者第九个希腊字母Iota的翻转。这是一个后高不圆唇元音，受前面的声母影响，发音时带有摩擦。汉学家用这个音标记录汉语，日本学家用来研究宫古岛（Miyako）语言的音系。

这个音可以用国际音标[ ͡ɯ]替代。普通话shi和si可以用近似的国际音标[ʂ͡ɨ] 和 [s͡ɯ]代替。

That is, shi and si would be narrowly transcribed [ʂ͡ɨ] and [s͡ɯ]. Kwan-hin Cheung, 1992. "北京話 '知' '資' 二韻國際音標寫法商榷" [IPA transcription of the so-called 'apical vowels' in Pekinese], in T. Lee, ed., Research on Chinese Linguistics in Hong Kong, Linguistic Society of Hong Kong.