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It's unclear if those who have nothing to do with a trademark can legally use them or not.
Google's policy document on the matter says “Google will not investigate or restrict the use of trademark terms in keywords, even if a trademark complaint is received.” The ad giant also advises advertisers seek legal counsel before using others' trademarks.
While we will not prevent use of trademarks as keywords in the affected regions, trademark owners will still be able to complain about the use of their trademark in ad text.
...With respect to use of trademarks in ad text in the affected regions, advertisers will be able to submit trademark complaints.