Most people have heard of a trademark before, and even if they don't know what a trademark is, they can probably recognize the iconic "TM" symbol near a logo, word or phrase. A trademark is actually quite simple: it signifies that the mark (may that be a logo, word, phrase or something else) is of a certain source and shouldn't be confused with other sources that may make similar products.
Trademarks don't protect against other companies making or selling the same product as a company that has a trademark. Rather, the trademark prevents other companies from using similar or confusingly identical logos, phrases and imagery to the company with the trademark. The other companies have an obvious incentive for doing this: they want to reap the benefits of the trademarked company's reputation. The company with the trademark obviously wants to protect that.
Registering a trademark can be a little complicated, but it is important to note that you still have rights even if you don't register the mark. However, getting the trademark registered is a very crucial step to protecting your company's identity.
The "TM" mark, though important, isn't the same as the "R in a circle" logo that you may see with many logos or marks. The R symbol means that the mark has been registered with the U.S. Patent and Trademark Office, and it is a warning to other people and companies that they shouldn't use logos, words or phrases that bare a striking similarity to the trademarked one.Â
Source: FindLaw, "What is a Trademark?," Accessed March 10, 2016