Label

In heraldry, the label is sub-ordinary in the shape of a horizontal line with three short lines (occasionally five) protruding from the bottom of it. It almost always appears on the chief of the shield.

In period heraldry it is a mark of cadence, indicating the first son, though this is not officially recognised in the SCA. A white label is used to distinguish the English Royal arms for the heir apparent, one of the rare cases where heraldry recognises white as a colour.
In some cases a label is itself charged with a further mark of cadence, to identify junior sons.