The United States Patent and Trademark Office ("USPTO") has been warning trademark customers about "unofficial" trademark solicitations for some time now. For example, each new trademark registration comes with a letter on orange paper warning of advertisements that are made to look like they actually came from the USPTO. More recently, the USPTO expanded the information on its website regarding such scams. The expanded page, http://www.uspto.gov/trademarks/solicitation_warnings.jsp, includes anecdotes of people who paid fees to these commercial entities thinking they were paying required fees to the USPTO. The webpage also includes examples of some of the almost-official names that have been used, like "United States Trademark Registration Office," "Patent Trademark Register," and "Trademark Renewal Service."
It's a good idea to talk to an attorney before attempting to register or maintain your trademarks yourself. If you decide to handle your trademarks on your own, these types of scams are just one of several reasons to be sure to do your homework first.