Why do noble families have coats of arms?

Families of great lords began using hereditary heraldic devices centred on the shield in the twelfth century, and their use spread to knightly families as a whole during the following century.
The primary purpose was recognition in battle, but they were very quickly also used on seals. In some countries, coats of arms also came to be assumed by townsmen (normally without a helmet, or with open helmet and mantling), but in others their use remained restricted to the nobility.

In countries where townsmen used arms with a helmet, the use of an open helmet was restricted to nobility whereas in countries where only the nobility used arms, open helmets might be restricted to the titled nobility.