Last year they made a change that made them so indistinguishable to the untrained eye that even Google rolled them back: https://techcrunch.com/2020/01/23/squint-and-youll-click-it/ https://www.cnbc.com/2020/01/24/google-will-iterate-the-desi...
But no, generally, they don't notice that. Studies have been done demonstrating how few users can tell the difference between an ad and a search result. In one study, half of respondents "didn't spot" ads in Google search results at all: https://www.123-reg.co.uk/blog/seo-2/how-google-is-profiting...
That study was in 2013, when Ads were much more obvious in search results than they are today. By 2018, the statistic of people who couldn't identify search ads on Google was up closer to two-thirds: https://marketingtechnews.net/news/2018/sep/06/two-thirds-pe...