Cap and bells the insignia of the professional jester.
cap of liberty a conical cap given to Roman slaves on emancipation, often used as a Republican symbol.
cap of maintenance a cap or hat worn as a symbol of dignity, or carried before a monarch on ceremonial occasions.
if the cap fits, wear it used with reference to the assumed suitability of a name or description to a person's behaviour. An earlier related reference in N. Breton's Pasquil's Fools-Cap (1600), makes it clear that the cap was originally a dunce's cap. (Compare if the shoe fits, wear it.) The saying is recorded from the mid 18th century.