It’s also not allowed to use someone else’s trademarks for <meta> tags and keywords in SEM campaigns.
An example: you write a code for your online shop and put eBay, Etsy, and Alibaba in the definition of metadata about an HTML document. It will be definitely seen as trademark infringement.
Regarding
Google Ads and search engine marketing, a case is not as apparent. In fact, search engines sell adwords to advertisers. And words registered as trademarks don’t really stand out in this set. A search engine sells it both for a trademark owner and its competitors.
However, this game with keywords should not confuse the customer. If the search results make the customer mess up the trademark owner and its competitor or consider them affiliated, there might be trademark abuse. ‘Oh, maybe, it’s their [others’ brand’s] new landing’ and so on.
In practice, courts deal with this SEM challenge to trademarks
in different ways, but the main thing they consider is an ecenomical loss. If the value of others’ trademarks drops because of your Google Ads campaign, you’ll probably get legal issues.
In any case, with a registered trademark, you will get a strong legal argument to solve a conflict with those who use your trademark as a keyword (if detected) in a pre-trial order or in a court.