I'm not confident I'm correct only because it seems unlikely Google would have a page listing trademarks it doesn't actually own. That being said, I'm pretty sure there's no other place to search for trademarks.
I also don't think there is actually a trademark on the term "Go" based on this USPTO search: http://tmsearch.uspto.gov/bin/showfield?f=toc&state=4809%3Ax.... But admittedly I've only looked through five or six pages; using the option to search for an exact term doesn't seem to cut down the search results at all.