Google recently debuted a new mobile search result that utilizes favicons. It didn’t take very long for curious webmasters to try and exploit it. It also resulted in imagery that Google didn’t want to display in its search results, like swastikas. Google responded by updating its software and Favicon Guidelines to exclude favicons that fall outside of its new guidelines.
This is the new guideline that directly affects the type of images that can appear in its mobile search results:
Google will not show any favicon that it deems inappropriate, including pornography or hate symbols (for example, swastikas). If this type of imagery is discovered within a favicon, Google will replace it with a default icon.Guidelines section from Define a favicon to show in search results via Google Search Central Documentation
Danny Sullivan, Google’s Public Search Liason, stated on Twitter that they didn’t anticipate what they consider to be the misuse of favicons, which prompted the new guidelines and quick software fix.