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 these references 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.
• If possible, design your arms in the style of your ethnic background. This will require you to research that country's heraldic style.
• Don't use symbols that have particular meaning in heraldry, such as crowns, coronets and supporters.
• Look for symbols that represent you as an individual, such as your occupation or hobby.

Downloadable Software
Achievement of Arms grammarman.www8.50megs.com/aboutachieve.html

Blazons! Software www.blazons.com/

Blazon and Blazon95 Software www.platypus.clara.net/blazon.htm