This saucer is of the same type as the Tong castle saucer now in The collection of the Worshipful Company. It is marginally smaller and lacks the Lombardic 'E' struck on the opposite side of the rim to the hammer mark. For related literature see the following publications: Pewter Society Journal Autumn 1978 S.Schemmel.
Journals of the Archeological society Vol 36.'The Medieval Pewterers of London' 1985 by Ron Homer
The Worshipful Company of Pewterers 1979 Cat S1/125 The Museum of London catalogue: Pewter A celebration of the Craft, 1989, fig 46, and figs 28-29 for two further saucers dated to circa 1500 but with different devices on the rim.
'The first recorded marks are those of the pewterer's hammer, probably a sign of quality or an indication that the item was made by a guild member.' A fourteenth century bowl (No.13) in the same exhibition catalogue has a crowned hammer mark on the front rim and a strengthening rim to top of the plate. The Notes for this read 'Recent study shows that the earliest plates from archeological sites have a strengthening edge on the upper side of the rim. Later plates have it below the rim' as in the present example.