Something along the lines of these:
I haven't seen one yet, but if one exists, that would be great.
I wouldn't call it a "social button" because of the connotation, I'd just call it an icon. That being said, yes someone's made one:
If you want to link to a user profile simply click the got flair? link on your user page:
We only do this on public betas.
for example on http://photos.stackexchange.com (currently in public beta)