Heraldry: Crests  

Crests are always very basic and are used to indicate the rank or status of the holder.  They originate from the circlets that were worn in battle around the helmets of warriors of noble rank and are generally shown immediately above the shield when the full Coat of Arms is displayed, such at above the door to the Manor House, or on a standard or pennant.

Ruling nobles use a 5 pointed golden coronet as their crest.
Other hereditary nobles use a three pointed golden coronet.
Non-hereditary nobles use a three pointed silver coronet.
Knights superior use their two tailed pennon as crest, the colour is not relevant.
Knights bachelor use their single tailed pennon, the colour is not relevant.
Sovereign states use a golden gate.
Towns and regions use a silver gate.
Ancient families and religious or chaptered orders may  use a black gate to represent their status.