Comment 11 for bug 1063453

http://www.ubuntu.com/aboutus/trademarkpolicy
http://www.linuxfoundation.org/programs/legal/trademark/sublicense-more

As far as Pidgin goes, I believe in many parts of the world, just using an identifying name is enough to get a trademark, although of course it wouldn't be a registered trademark unless it is actually formally registered.

I have several books that mention Windows or Linux, I have read countless news, magazine, and web articles, and I stand by my assertion that these symbols are only rarely used, first mention or otherwise.

A simple disclaimer is fine; anything else will cause significant inconsistency with pretty much zero benefit.