Copied from the Welcome and Help Forum:
"What are microbadges and how do I get them?
A small icon that identifies your favorite interests and forums. If you click on the microbadge, you'll see a list of people who also have that microbadge. You can hover your mouse over a microbadge and see what the badge stands for. Badges can be purchased for 5 acorns each. You can also choose what order you want your badges displayed. The purchasing and manipulating of the microbadges can be handled in your profile."
Hope this helps.
