Several prospective TLD applicants have filed trademark applications for TLD strings over the past year. Obviously this has been done in order to give the TLD applicant an advantage should a "string contension" arise. Trademark applications have been filed for .music, .kids, .books, .buy to name a few.
A paper addressing problems involved in registrating TLD strings as trademarks have been published by Michael Palage and you can read it here
New gTLDs: Let the Gaming Begin, Part I: TLD Front Running