Prominently? Bold text?
Here's how they repeatedly made ads indistinguishable from search results: https://atechnocratblog.wordpress.com/2016/07/26/color-fade-...
Or this: https://twitter.com/garybernhardt/status/1648496387640938496
To quote from the above, here's what they said in the beginning: "we expect that advertising funded search engines will be inherently biased towards the advertisers and away from the needs of the consumers"