M.L. West, 'Burning Sappho', Maia 20 (1970) 307-330 at 310 (= Hellenica, volume II: Lyric and Drama, 31), note 5, comments as follows on Sapph.1.20:
"I have preferred Σάπφ', persuaded by G. Zuntz (Mus. Helv. 8 (1951), 16-22) that that Ψ was an early misinterpretation of a sibilant ɯ or m [these are not the characters as they appear in West's article, but the nearest approximates that I can find] (ṣ, tsade) used by Sappho in spelling her own (Asiatic) name. The argument does not fall if Lesbos had the ψ sign with the same value as the Ionian alphabets (L.H. Jeffery, The Local Scripts of Archaic Greece (Oxford 1961), 361).-- I print Meillet's elegant ἀδίκησι to advertise it, but ἀδικήει may be right.".
The coin from Mytilene has been discussed online by the British Museum. Cf. the comment in Pollux IX 84 (test. 11 Campbell) on such coins and see Richter, Portraits of the Greeks, i: 70-72, for images and full ancient references and modern(ish) bibliography.
Of particular interest is the occurrence of the name on IG XI (2) 199 B.18: ἄλλον δακτύλιον ἔχοντα ἀνθράκιον Σαφφοῦς,... (V1-84351 in LGPN).
Also of particular interest is the single instance of the compound name Σαπφόδωρος, as a nickname (ὁ καὶ Σ.), in an inscription of the Roman period from Lycia.
Other celebrities feature on coins, especially in the Roman period.
From a different starting point, note that Δικάπφω (inscription) is the only other name reported by LGPN that ends in -απφω. There is one instance of Κορίφφω.