Ah, the cease and desist letter. There is no more trusty weapon in the arsenal of an entertainment lawyer.
Most of these letters will get the job done, but tend to be dry and uninspired. They often appear to have been cribbed from a set of legal Mad Libs:
This letter will serve as formal notice that the above-referenced company is the legal owner of _____[noun]_____. It has come to our attention that you are _____[verb ending in -ing]_____. We hereby demand that you _____[verb]_____. Should you fail to _____[verb]_____, we will _____[scary-sounding verb]_____. Govern yourselves accordingly.