Registered trademark and other trademark symbols
The ® (R in a circle) symbol is used to denote registered trademarks. Consistently using it together with one’s own trademark is generally considered good practice. Making it clear that certain words or graphics are registered trademarks protects them against becoming generic in the sense that they no longer identify a specific origin for the product (also called “genericide”). Using the symbol also makes it more difficult for others to use ignorance as a defense in trademark infringement cases. The ® symbol is also commonly used to acknowledge the existence of third-party trademark rights, whether in marketing materials or works of reference.
In some jurisdictions, such as the United Kingdom, use of the ® symbol without an actual registration is specifically illegal, and in other jurisdictions doing so may be considered as misleading advertising even if not specifically regulated.
The ® symbol is generally not based on an explicit legal definition, its use is conventional and supported by precedent. In this respect, it is different from the copyright symbol © (C in a circle), defined in Article III of the Universal Copyright Convention, and the record producer/performer symbol ℗ (P in a circle), defined in Article 11 of the Rome Convention, for example.
Typographically the ® symbol and the other trademark symbols are usually used as a small superscript sign immediately after the mark, and the appearance of these characters in most fonts is designed accordingly. Again, here the © and ℗ symbols are different, as they are used as “words” in their own right and designed accordingly (approximately same height and alignment as capital letters).
The ™ (superscript TM: trademark) symbol is used to denote trademarks in general. Using the symbol shows that at least its user considers the attached mark to be a trademark, but makes no claims as to its registration status. It is a good idea to use the symbol whenever you are considering registration for a given mark or your application for registration is already pending. Using the sign may also help in gaining distinctiveness for a mark which is initially not registrable because it is too descriptive.
The ℠ (superscript SM: service mark) symbol carries the same basic meaning as the ™ sign, but it is used for unregistered service marks, that is, trademarks for services rather than tangible goods. It is generally only used in the United States. In other jurisdictions, the ™ sign is used for both goods and services.
For your typing convenience
|®||U+00AE REGISTERED SIGN||Alt+0174||Alt+r||®||C-x 8 R|
|™||U+2122 TRADE MARK SIGN||Alt+8482||Alt+2||™||C-q 2 0 4 4 2 RET|
|℠||U+2120 SERVICE MARK||Alt+8480||℠||C-q 2 0 4 4 0 RET|
|©||U+00A9 COPYRIGHT SIGN||Alt+0169||Alt+g||©||C-x 8 C|
|℗||U+2117 SOUND RECORDING COPYRIGHT||Alt+8471||℗||C-q 2 0 4 2 7 RET|
NB: On Windows, you must press and hold the Alt key for the whole sequence, and the character codes must be typed on the numerical keypad. Typing the numbers on the top row of the regular keyboard will not work. The Mac codes are for the US layout, but at least the Alt+r combination works for many others as well.