I am not an attorney and any comments I post are not intended, nor should they be construed, as legal advice. If you need legal advice, please consult a legal expert who is familiar with the area of legal expertise you need.
I noticed a comment in a social media group where someone was wanting to use a trademark symbol for a product that was not trademarked. The poster did not indicate if they wanted to use TM or the ® symbol. There is a difference between the two symbols and TM can be used for an unregistered trademark. To use the ® symbol, the trademark has to be registered with the appropriate government agency . In the U. S., to use the ® symbol, it needs to be a registered trademark that has been approved by the Trademark Office – https://www.uspto.gov/. To use the ® symbol if the trademark has not been registered can cause the person all sorts of legal issues that aren’t worth it. It’s not a cheap process to register a trademark, but it can be worth it.
Be warned some things can’t be trademarked – https://en.wikipedia.org/wiki/List_of_United_States_Supreme_Court_trademark_case_law. Here’s a PDF put out by the Trademark Office – https://www.uspto.gov/sites/default/files/documents/BasicFacts.pdf. Also, if an existing trademark is close enough to your planned trademark, your trademark application probably won’t be approved. You can do a search using the Trademark Office or PDF above to look for existing trademarks.
One thing a trademark cannot do is extend copyright. A number of companies have tried to use trademark to extend copyright past its expiration date. In the U. S., the Supreme Court has made it clear in numerous rulings, trademark can’t be used to extend copyright. That doesn’t mean a person can use someone else’s trademark without permission. Let’s use Company D – it has trademarks for various items and it has numerous books, movies, etc. that are covered by copyright. Some of those copyrighted items are set to expire in the near future. I expect Company D to try and use trademark to extend copyright.