(First Share) Shared a topic that got clicked on. Why? Sharing topics with the outside world (using the share button and the URL that has your username on it) is how we attract new blood to any community.
Edit: So to get this badge you need to click the share (chain) icon next to the heart icon on posts and give the link to someone - e.g another forum or chat group (skype).
Since that url has your username at the end if someone clicks on it it'll give you the badge.
I.e I believe I probably gave you the badge when I clicked on this link: