Sumptuary law
Sumptuary Law is a list of rules controlling what people of varying classes were and were not allowed to wear, as fit their social station. Medieval sumptary laws varied and tended to become more elaborate as the period progressed. Dressing above one's station was a criminal offence, and an assault on the rigid social order of feudalism.
Similar laws were sometimes established for other matters, e.g. ownership of birds in falconry.
There is some evidence to suggest that the sumptuary laws were frequently, if surreptiously, broken.
Sumptuary Law in the SCA
The SCA has very few formal sumptuary laws. SCAdians can wear whatever garb they wish, with certain limitations. Only the Chivalry can wear a plain white belt or baldric, only peers can wear the emblems of their order of peerage, only nobility can wear elaborate coronets, and it is very impolite to wear another's arms without leave.