Sometimes people will suggest looking at other people’s SCA devices (whether in person or on an SCA Kingdom’s roll or arms) for inspiration for your heraldry. This can be quite misleading, as some devices were registered quite a while ago when the heralds knew a lot less about period heraldry, and some of the things you see in devices will not be possible to register in a device today (link to above). It can also be a poor idea because just as your average fighter and your costume laurel have radically different levels of accuracy and artistry in their clothing, so devices range greatly in authenticity, and it’s not easy to pick which are good examples of heraldry. A lot of SCA devices, while technically within the rules, are overly complicated and modern looking.
A good place to look for examples of heraldry are period heraldic rolls of arms (More). From the 13th Century onwards, quite a lot of Rolls of Arms were produced in Europe, listing the arms belonging to various nobles, often accompanied by pictures of those arms.