Apparently complete in a single letter: A; np letters to either side. Upside down to vessel.
Single alphas are often found on objects dedicated to Athena, undoubtedly as abbreviations of the goddess' ... Single alphas are often found on objects dedicated to Athena, undoubtedly as abbreviations of the goddess' name (cf., for example, those from the sanctuary of Athena on the acropolis of Sparta: B.S.A. 30, 1928-1930, p. 251, fig. 6, nos. 1-11, 14, 22).