Verify Trademarks

https://tmsearch.uspto.gov/bin/gate.exe?f=login&p_lang=english&p_d=trmk

TRADEMARK ELECTRONIC SEARCH SYSTEM (TESS)

This is a US government website pertaining to Trademarks. You may search for words or key phrases to find if they are registered as a trademark or not in the US. This is very useful when you are for example self-publishing books. Always check if the title you've decided on is trademarked already or not.