Show ownership of your document, logo, or name. You may do so by adding a copyright or trademark symbol to your word document. This comes in handy if you have a business, invention, or name that is owned by you. By symbolizing this within a word document when writing to others, it conveys that it is copyrighted or trademarked and cannot be used by others unless they have your authority. Basically, it protects your own interest.
Additional resource: How to apply for an International Trademark Easily?
Here’s how to add a copyright or trademark within Microsoft Word 2007: 
1. Choose the “Insert” tab on the top.
2. Go to the “Symbols” group and select “Symbol”
3. You may select the TM for Trademark and © for Copyright
Of course, there are other symbols you may use. Other types of symbols may be selected by going to the Subset drop-down box at the top-right.