Protect your work. Just a few suggestions.
1. Add EXIF information to a few of your images. It doesn't have to be added to all of them, but adding this to a few images that are uniquely yours, can help identify a template as your original work if a copy appears in the market.
2. Add some code or CSS that does absolutely nothing. Most people don't know this, but map makers have been adding non existent streets to maps for years to help identify unauthorized copies. If you've put a lot of work into the css for your template, why not use this old map maker trick to help identify it as yours? Add some CSS that does absolutely nothing, but can help identify the css document as a whole, as belonging to you.
While you're at it, why not add some php code or html code that does absolutely nothing?
Those are two things that pop into my head as ways to help identify your work. If anyone has more ideas, let's hear 'em.