Always learning something new.
Many artists operate under the assumption that saying something is copyright (or putting the cute c in a circle on a piece) protects the work. While copyright exists at the time you create a piece, it doesn’t hold up in court.
If you have a piece of artwork, or a design, you fear will be used for someone else’s profit (read: you might end up in a lawsuit someday), you should consider registering your piece with the Copyright Office. For details about the fees (starting at $35) and channels to pursue copyright registration, please visit the Copyright Office on the web or download their handy circular – www.copyright.gov/circs/circ40.pdf