Copyright, Trademark and Patent: Protecting IP for Independent Designers
What designers should do in relation to protecting their designs when showing them to others is, for obvious reasons, a concern for many starting designers. The short answer is, don't worry, you don't actually need to do anything. There is a good deal of professional advice freely available on this subject to anyone with access to a library and I would strongly suggest referring there if you have any worries or doubts. My opinions are formed from a range of sources but two excellent places to start are the "For Dummies" range of books for general legal advice and Jeremy Holcomb's "White Box Essays" for an industry specific view point.
I'm not going to try to give advice for all people, because I'm not an IP (Intellectual Property) lawyer, my advice is intended to be applicable primarily to being a small or first time independent games designer. Quite simply different things are practically possible or realistic for a major company selling tens or hundreds of thousands of units than for a first time designer or self-publisher who will be lucky to sell their first thousand.