The icon denotes a post that includes a discussion on peer-reviewed research, and is intended to distinguish such posts from other posts that often appear on blogs. It (and several other similar icons) was designed for the Bloggers for the Peer-Reviewed Research Reporting (BPR3) initiative, which was spearheaded by Dave Munger.
Posts featuring the icons will be aggregated in categories at the BPR3 website, so that they can be found easily by anyone looking for good quality blogging about peer-reviewed research. There are already dozens of bloggers using the icons, and many more are likely to start doing so.
Use of the icons isn't restricted to us here at ScienceBlogs.com, so if you write about peer-reviewed research on your blog, then feel free to display one of them on the appropriate posts.