It was announced on Google+ by Google’s Zineb Ait Bahajji that Google’s mobile search results snippets are going to show a message to searchers if Google is not able to show the snippet because the webmaster is blocking their crawlers.
This feature was first added to desktop search in August of 2012, and if a webmaster wanted to block GoogleBot and Google tried showing that URL in the search results, a message would appear in the results as to why there were unable to show a full snippet.
Google has decided to finally bring this feature to mobile search results. This feature will appear when the mobile version is blocking Google, and the desktop version is fully crawlable.
An example given by Barry Schwartz, if a search in Google shows the desktop version that displays the full snippet, but the mobile version has a blocked snippet. The message that Google displays reads “A description for this result is not available because of this site’s robots.txt – learn more.” The learn more link goes to this page.
This is what the mobile version looks like:
Here is the desktop version: