You may certainly
design your own coat of arms, and there's even computer software to
help you do so (see below). You can also have it registered with the
American College of Heraldry <
users. aol.com/ballywoodn/acheraldry.html>, which recommends you follow these guidelines when designing your own:
Make sure your design is unique. Check other crests to make sure you are not infringing on someone else's design.
Keep the design simple; the idea is to have it be easily recognized as yours and remembered.