σφραγιστήριον
From LSJ
ἢ λέγε τι σιγῆς κρεῖττον ἢ σιγὴν ἔχε → either say something better than silence or keep silence (Menander)
English (LSJ)
τό, A seal, stamp, PLond.5.1657.13 (iv/v A.D.); = signaculum, signatorium, Gloss.
German (Pape)
[Seite 1052] τό, Siegel, Petschaft, Sp.