[In "Opuscula Anatolica IV", NC Vol. 174 (2014), pp. 1-28, there is a chapter by Philip Kinns called "Lunate letter forms in the 4th century and Hellenistic coinage of Ionia".
He shows that the use of the lunate forms of sigma, omega and epsilon on coins began already in the forth century BC (for some of these letters earlier, for some later) and have been used in parallel to the usual forms.
That is considerably earlier than I was aware of, for coins. Thank you for the Opuscula Anatolica IV
article, it is quite an interesting read.