Write trademarked names in a novel, but don't use an R enclosed in a circle to indicate the name or phrase is trademarked. Following trademarked names with the symbol indicating the trademark is not aesthetically pleasing in the pages of a novel. In fact, it would be distracting. According to the United States Trademark Office, there is no federal law that requires use of the trademark symbol after use of a trademark name or phrase. It is not customary for novelists to use them. There may be a state law requiring the use of the trademark symbol, so consult the laws for your state.
Use registration marks properly if you use them. The R enclosed in a circle can only be used if a trademark truly is registered. TM enclosed in a circle is used when a registration is pending. A search of the United States Trademark website will give official trademark information. The correct way to write a trademark name is by capitalizing the proper noun and following it with the generic. An example of this would be Jell-O brand gelatin. This isn't required by law either.
Include a page at the front of your book that lists registered trademark names you use frequently in your book, along with the trademark symbol.This is not a requirement by law either, but it is a courtesy. Doing so is a way of showing respect for the trademark without breaking the flow of the text in your novel with trademark symbols each time one of your characters visits McDonald for lunch.