Do you trademark your brand / app name / business?
lionhearted: In the USA, you can use (TM) without any filing as long as no one else has a claim to your mark. You need to pay and do the filing process for a Registered Trademark, which carries a bit extra weight and allows you to use (R). (TM) is probably fine, and in my opinion - more recognizable. The (R) is good if you're a bit smaller and competitors might consider for gunning for you/misrepresenting.For instance, Salesforce.com has the (R) going on:
http://salesforce.comGmail is doing the (TM):
http://mail.google.comMy rough intuition is that the bigger you are, the better slapping (TM) on works, even if you're registered. Both (R) and (TM) add credibility, but I think the (R) works better as deterrent to somewhat savvy competitors, whereas the (TM) might be more recognized by consumers. Most people know that TM is trademark, and don't know what (R) means.