These devices are not acquired by the mere inheritance of the same family line, but must be granted. In Scotland, the authority for the granting of Arms is the Lord Lyon, and the grant is made to an individual and not to a collective family.
Before the 1100s there was no proper recording of the devices that knights and barons chose, to decorate their shields and banners. Systematic heraldry and its recording did not really come in until the cult of "chivalry" became fashionable in the mid-1100s (symbolised by the writing down and wide circulation of the legends of Roland in France, and Arthur in England).
The "coat of arms" is owned by the individual to whom it was granted, and subsequent descendants do not automatically inherit that right. There have been successful prosecutions, both in England and in Scotland, following the illegal display of Arms.
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