How can you stop a client from (TM)ing you work?

I was recently searching through a trade magazine, and discovered a new ad for an old client of mine. In it was a phrase that I coined for the cover of a brochure that I designed for them. At the end of the phrase was (SM) so I am assuming that they in some way sought or are seeking exclusive usage rights without consulting or compensating me for their additional usage. What can I do to stop their unauthorized usage and service marking of the phrase.

Thank you for your response.