When thinking about whether or not to enforce a trademark, keep in mind the purpose of having the mark is to serve as an identifier of the source of the good or service for consumers. With this in mind, in order to preserve your own rights to a mark you have to try to maintain its strength as an identifier for your product.
In the event you have adopted a mark, an important part of maintaining it is to monitor the marketplace for others using identical or similar marks for the same or similar services. In the event you locate someone using the mark in a way that might cause consumer confusion, steps should be taken to eliminate potentially weakening of the mark. Consideration should be given to sending a letter advising the infringing user of your prior use and demanding that they stop using the mark (sometime referred to as a cease and desist letter). Before sending such a letter, you should consider discussing the matter with an attorney for their help in evaluating the mark you are seeking to protect – there is nothing worse than demanding someone else stop using a mark, only to find out that they have a greater right to use the mark than you do. If the infringer fails to heed your warning, you will need to evaluate how widespread the infringement is and make a business decision about whether to proceed to litigation.