The National Gallery has a short little primer on paintings of saints and recognizing them by means of their attributes. As an example, in the painting below Saint Genevieve of Paris holds the candle which she miraculously relit. On the brooch at her neck are the alpha and omega signs. Saint Apollonia of Alexandria’s brooch shows pincers: she was tortured by having her teeth extracted.
Saints Genevieve and Apollonia (1506) Oil on lime, 120.5 x 63 cm
Bought, 1987; NG6511.1
This painting is part of the group: ‘The St Catherine Altarpiece: Reverses of Shutters’ (NG6511.1-NG6511.2)
http://www.nationalgallery.org.uk/paintings/NG6511.1