A billet is a brief letter or document. In period armory, it is most often found strewn in a semy field; this is its earliest usage, dating from c.1255 in the arms of Gascelyn [ANA2 191]. However, billets are also found as distinct charges; such usage can be dated to 1445, in the arms of Livingstone [DBA2 127].
The billet is drawn as a rectangle, with no detail or shading, much like a polygon; it is upright by default. Period armory seems to have considered the billet and the delf to be equivalent, and no difference is granted between them in Society heraldry. At one point, billets with complex lines (e.g., a “billet embattled”) were permitted in Society heraldry, but pending evidence, these are no longer allowed.
The Registrar of the Society bears: Vert, in pale three billets argent winged Or.
Raymond Norgate bears: Argent billety sable.
Aeddan ap Trahaearn bears: Per fess argent and vert, three billets fesswise counterchanged.