I also found this:
"The owner of a trademark may pursue legal action against trademark infringement. Most countries require formal registration of a trademark as a precondition for pursuing this type of action. The United States, Canada and other countries also recognize common law trademark rights, which means action can be taken to protect an unregistered trademark if it is in use. Still, common law trademarks offer the holder in general less legal protection than registered trademarks."
™ (the "trademark symbol", which is the letters "TM" in superscript, for an unregistered trademark, a mark used to promote or brand goods)
℠ (which is the letters "SM" in superscript, for an unregistered service mark, a mark used to promote or brand services)
® (the letter "R" surrounded by a circle, for a registered trademark)
