A trademark is a source identifier: it tells the public that these products and services come from your company. The use of the appropriate trademark symbol - TM, SM or Ⓡ - next to your mark gives notice to consumers that your trademark is a trademark, that these aren't just words or designs.
Accordingly, the purpose of using a trademark symbol is to notify others of your claim to rights in your mark and to discourage them from using it or a similar mark for the same or similar products or services. It it advisable to use one of these symbols, just be sure you're using the right one and using it in the right way.
What do TM, SM and Ⓡ mean?
The TM and SM symbols are used for trademarks and service marks which are not registered with the U.S. Patent & Trademark Office ("USPTO"). This applies to trademarks which are (a) only in use (not registered); (b) the subject of a pending trademark application with the USPTO; or (c) pending or registered with a state trademark registry. TM means "trademark" and is used with marks which apply to products; SM means "service mark" and is used with marks which apply to services. If your mark covers both goods and services, you can simply use the TM symbol. While there is no requirement to use either the TM or SM symbols, it is highly advisable to do so. Note that use of the TM and SM symbols does not guarantee that your will be protected; it is simply a mechanism for providing notice.
Unlike the TM and SM symbols, the Ⓡ symbol is reserved for federally registered trademarks or service marks only. This means that, in order to use the Ⓡ symbol, your trademark must be registered with the USPTO. If you have filed a federal trademark application and it's pending (not yet registered), you may only use the TM or SM symbol until the USPTO issues your registration. A registration with a state trademark office does not convey the right to the Ⓡ symbol, so only the TM and SM symbols may be used.
As with unregistered marks, there is no legal requirement to use the Ⓡ for a federally registered mark. However, there are distinct legal advantages for doing so and legal consequences for failing to do so. If you have acquired a federal trademark registration, it makes sense to use the Ⓡ symbol.
How should the symbols be used?
While there are not set legal requirements for where you should place any of these symbols, it is advisable that you follow customary practices and do one of the following: use the appropriate symbol in superscript to the upper right-hand side of your mark or down to the lower right-hand side of your mark. Avoid placing it to the left, top or underneath your mark. Again, the idea here is to provide notice to the public of your ownership of the mark, so it should be placed where it is most likely to be recognized as trademark notice.
In places where you mention your trademark, like the text of written paragraphs (for example, a press release, a paragraph on your website, or a marketing brochure), it's customary to use the appropriate symbol the first time you use your mark or where it appears most prominently. In this context, you do not have to use the symbol each time you use the mark, and so can avoid the clutter and visual distraction that such symbols can create. That being said, you may want to use some distinguishing element(s) with your mark, like a different font, size, and/or color or all caps or italics, so that it doesn't look like the plain text around it. In addition, in each communication, you may want to identify the product or service to which your mark applies immediately after your mark, so that its application is clear to the reader (for example, iPad® tablet or Tesla® car). One other option is to include a sentence about your trademark ownership (for example, "iPad® and iPhone® are Registered Trademarks of Apple, Inc.") somewhere on that document or your website (for example, in the footer).