Jen - I agree with Eli. It's best not to use the TM symbol in a URL string - it will confuse the end user when it's URL encoded and scrambled. Rather, put the mark on your pages and in images.
If you have gone through the registration process with the USPTO (United States Patent and Trademark Office), you should be using the symbol next to your mark, and not the TM symbol.
According to the Trademark FAQs on the USPTO site: http://www.uspto.gov/faq/trademarks.jsp#_Toc275426682
Do federal regulations govern the use of the designations "TM" or "SM" or the symbol?
If you claim rights to use a mark, you may use the "TM" (trademark) or "SM" (service mark) designation to alert the public to your claim of a “common-law” mark. No registration is necessary to use a "TM" or "SM" symbol and you may continue to use these symbols even if the USPTO refuses to register your mark. Those symbols put people on notice that you claim rights in the mark, although common law doesn't give you all the rights and benefits of federal registration.
You may only use the federal registration symbol "" after the USPTO actually registers a mark, not while an application is pending. And it may only be used on or in connection with the goods/services listed in the federal trademark registration and while the registration is still alive (you may not continue to use it if you don’t maintain the registration or it expires). Although there are no specific requirements on where the symbol should be placed relative to the mark, most businesses use the symbol in the upper right corner of the mark. Note: Because several foreign countries use “
” to indicate that a mark is registered in that country, use of the symbol by the holder of a foreign registration may be proper.
From another section_: There are no specific requirements on where the “” symbol should be placed relative to the mark, but most businesses use the symbol in the upper right corner of the mark._
Hope this helps!
-- Jeff