Should I Register My Domain Name as a Trademark?

Dear Rich: In your book on trademarks there is a discussion of whether you should register "trademark.com" as a trademark if you've already registered "trademark." The example provided is a line of menswear that is now also going to be sold online. The conclusion is that you should consider registering the full domain name (trademark.com) if establishing services or goods unique to the Internet business. Could you please explain why? If the PTO considers the ".com" piece of the trademark as unprotectable, what benefit would be gained by registering the full domain name? If you have a business that only sells online, should you register both "trademark" and "trademark.com"? 
If you register a domain name as a trademark with the USPTO, you won't be able to claim any rights to the ".com" (known as a top level domain or gTLD) by itself. The USPTO considers elements of the domain address such as "http://" and  "www." and gTLDs as unprotectable features of the website address. Although they are unprotectable by themselves -- that is, you can't stop others from using .com --  a mark that combines these elements with a protectable term is registrable if it is unique to an Internet business.
More than an address. The main thing to keep in mind is that you should register the .com if it is more than an address, that is if it is a source-indicating trademark use. For example, Zappos.com, an online footwear and clothing company refers to itself as "Zappos.com" at its site. In this way, Zappos.com, like Amazon.com, is more than an address on the web, it's the brand itself. (The USPTO's Trademark Examining Rules for domain names are located here.) The benefit of registering .com depends on the company. Some want a deep trademark portfolio, one that enables the broadest claim to trademark rights. Amazon has registered over a hundred "Amazon" marks and about 25 "amazon.com" marks (12 of which are still live). For smaller businesses, it may not matter much whether you register with or without the .com.
One more quirk. When registering a domain name, an applicant is permitted to furnish a drawing of the term within the address. For example, if registering Amazon.com, the applicant could furnish a drawing of the term "Amazon." (See TMEP Sec. 1215.02(c)))