1) Heraldic charge 
Fetterlock is a sort of shackle which is a common charge in heraldry, often displayed in a way resembling a padlock. Edward IV used a heraldic badge consisting of a fetterlock and a falcon. This was originally the badge of the first Duke of York, Edmund Langley, who used the falcon of the Plantagenets in a golden fetterlock. This was also used by ...
padlock