A well-designed user guide contains a copyright page, which provides copyright and trademark information for your company's products as well as for any third-party products mentioned in your document.
Start with the copyright notice for the document followed by the trademark notices for your company's products (only those that are mentioned in the document) and the address of your company. Follow this with the notices for third-party products.
Since many companies consult lawyers when they write their copyright and trademark notices, ensure that your notices for third-party products are written exactly as required by the third party. Many companies provide this information on the legal pages of their web sites; even so, expect to spend quite a lot of time researching copyright information. To save other writers the bother of duplicating this research, it is a good idea to create a database of copyright information so that writers can just copy and paste the notices as required.
It is not necessary to use both the word Copyright and the C-in-a-circle symbol. One or the other will do, but the symbol is preferred. The symbol is followed by the date (or dates, starting with the earliest and separated by commas), which is followed by the company name followed by a period. You can follow this with "All rights reserved." Here is an example of a copyright notice: