In 2004 and 2005, GEICO Insurance sued Google to stop GEICO's competitors from buying Google ads that appear when users search for GEICO. The court ruled that Google has a right to sell such ads, even though GEICO is a trademarked term. However the court also ruled that the actual advertisements that appear must not use the trademarked name GEICO.
Other lawsuits are still pending, and Google has lost one similar case in France as of this writing.
I am not a lawyer and cannot give legal advice. If you have serious legal concerns, consult a lawyer.
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