Have I ranted about this lately? A “trademark” is a word, symbol or other indicator of the source and quality of goods or services, i.e., a noun. Something can only serve as a trademark if it becomes associated by some segment of the public with a particular source. When it ceases to do that (perhaps by becoming generic, like aspirin) it is no longer a trademark. One may use such an indicator in the hope that it will become recognized as a trademark, and one may apply to the government to register your claim that it is your trademark, but one cannot trademark (verb, transitive) it.
What prompts this admittedly peevish, pedantic post? A Reuters report this afternoon carries the headline “Apple Trademarks Design of its Retail Stores.” Not so. Apple applied to register its claim that the design of its retail stores (their “trade dress”)—including such features as “a clear glass storefront surrounded by a paneled facade” and an “oblong table with stools…set below video screens flush mounted on the back wall”—is sufficiently distinctive to function as a trademark, and the U.S. Patent and Trademark Office, Reuters reports, has granted that registration. (A copy of which is here.) Registration carries with it significant legal advantages, but it cannot turn that which does not actually function as a trademark in marketplace into a trademark. Reporters and headline writers, please take note.