Numerous posters wouldn't pick this particular charity, even if it happened to be among the best, unless they were motivated by signaling aspirations rather than the rational choice of the best recipient.

You know this is a blog started by and run by Eliezer Yudkowsky - right? Many of the posters are fans. Looking at the rest of this thread, signaling seems to be involved in large quantities - but consider also the fact that there is a sampling bias.