The symbols ®, TM and SM provide notice to the world that you are claiming trademark rights in any mark using these symbols. You may use the TM on marks identifying goods, and the SM on marks identifying services. You need not have a federal or state registration to use the TM or SM symbols. However, the ® symbol, which provides "statutory notice" can only be used if your mark is federally registered on either the Principal or Supplemental Registers maintained by the United States Patent and Trademark Office (USPTO).
You do not need to use the ® symbol in order to provide notice of your trademark rights. You may also use the phrase, "Reg. U.S. Pat. & Tm. Off." or "Registered in the U.S. Patent and Trademark Office." Or, you may place the phrase at the bottom of a page when using an asterisk next to the mark that refers the reader to the phrase at the bottom. Thus the NutraSweet Company could put an asterisk next to their red & white swirl logo, and a phrase at the bottom or side of a page that read: "Reg. U.S. Pat. & Tm. Off." or "NutraSweet is a registered trademark of NutraSweet Co."
Advantages providing notice:
There is no requirement that you use any of the symbols, however there are two important advantages to using them. First, the symbols provide notice to the world that you are claiming the symbols as trademarks, and this will deter others from attempting to use the name for their own business. Second, if you ever find yourself in a lawsuit for infringement of your mark, and you haven't used the statutory notice (i.e. the ® symbol), then you won't be able to sue for damages or profits unless you can prove that the infringer had actual notice of your trademark rights.
Unauthorized use of the ® symbol
Unauthorized use of the ® can result in penalties, unless you can show that the unauthorized use was a good-faith mistake. Inadvertent unauthorized use can occur when the USPTO cancels your mark without your knowledge. It is quite likely that your labels and materials will still display the ® when the cancellation issues, thereby leaving you vulnerable to an attack that you were acting in bad faith and should be penalized for unauthorized use.