From above link check which campaign is eligible to your rank.
After you get a rank,join a signature campaign by applying through there thread/post (format is written there how to apply).
After you got applied then copy the respective code according to your rank.
Then go profile>forum profile information>paste the signature(code) in signature section>then save(change profile option in the bottom).
You are all set now,post the required number(minimum -maximum) of post.
you can check you activity/posts by clicking you name.
