I often advise clients to use the TM (for physical products) and the SM (for services) symbols next to their brand or product name. This serves many purposes, but mainly to tell the public that you consider that word/logo as your brand, as a “no trespassing sign” to competitors, and as evidence in any future litigation on trademark infringement. On the last two points, the TM/SM symbols prevent arguments of ignorance, for example, “We didn’t know that word/logo was a trademark”.
The circle ® symbol may only be used in the U.S. on trademarks which have been registered at the US Patent and Trademark Office (USPTO). State trademark registration is insufficient. U.S. courts have also upheld the use of the ® symbol in the U.S. for trademarks already registered in another country. If you are a U.S. brand doing business outside of the country, be wary of countries with civil and even criminal penalties for using the ® symbol on a brand which is not registered in that country.
Use of the ® symbol is recommended when possible because it provides “actual notice” that a trademark is registered. Not using it won’t create an absolute defense for an infringer, however, in a suit for damages only damages and lost profits occurring after actual notice can be recovered. Besides using the ® symbol, actual notice is also given in a cease-and-desist letter, which could be another point in time from which damages/lost profits may be calculated. This means that if you receive a cease-and-desist letter about infringement of a mark, and you did not know of the existence of that mark prior to the letter, you may be able to limit your financial liability to the damages/lost profits occurring after you received the letter.
Takeaway: As a brand owner, use the TM and SM symbols next to your brand until it is registered as a trademark. After registration, use the ® symbol.