Whether an ad appearing alongside organic search results for a search consisting of a trademark, creates a likelihood of confusion with that trademark, may depend in part on the user’s ability to distinguish what on the search results page is an organic result and what is a paid result.
Publicly available research in the topic is sparse and of questionable methodology. However, for what it’s worth, such research suggested that users were not easily distinguishing between paid and organic search. However, with the growing public awareness of Google and paid search in general, it may be the case that this research is out-dated.
Be that as it may, it is likely a step backward that it appears that today Google increased the size of the Adwords font so that it is the same size of the organic results.
Google screenshot from Bizresearch.