Google seems to be testing a file type Label in the search results snippets. Sergio Redondo posted a screen shot on Twitter of him being shown a PDF label icon in the Google search results on a snippet. The label communicates to the searcher that clicking on that result will not take you to a web page but rather a PDF document.

Here is his screen shot:

I personally cannot replicate this but Google is constantly conducting user interface tests and this is just one more of the many they conduct on a daily, hourly, minute by minute basis.

Personally, I like this one.

Forum discussion at Twitter.