RT means it is a registered trademark, so that word was registered with the U.S. Patent Office. You would normally see it as registered if you do a trademark search. TM just means they own the name, but it may or may not be registered. RT has a lot more power in terms of protecting it in court, or giving the person full rights to it in case it is being abused, such as another company selling a product with the same name, using a website with that name, etc.
