The SCA heraldry organisation is loosely based on that set up in England by King Richard III in 1488.
A device is built up following the specific historical rules (with a few add ons), and described by its very own language 'BLAZON' based on Norman French.
The SCA maintains the world’s largest record of individual devices in the world, approximately 20,000 of them. To the left you can see the device (pending) of Glen Rathlin and to the right the SCA Kingdom of Drachenwald.
The link above ‘Heraldry 101’covers the very basics of device design and heraldic history.