Yes you should copyright your patterns! I have published 3 patterns and copyrighted each one by using the copyright office in Washington D.C. There is a charge for it. Check with the website to see how much. You fill out the paperwork, send a copy of your pattern and a check for the fee and mail it in. It will take about 6 months or so but you will receive the copyright papers on it. It is always best to protect your design. You worked hard to perfect it and you should have the recognition that goes with it. It is illegal to copy any published patterns!