im interested in joining a sig campaign.. how am i able to join? can u pls help me with this? im still new in here and i want to earn some bits.. thanks! 
Basically what Norrisk said, go to his link and see if there is a campaign that is hiring Newbies. For newcomers I would personally recommend 777Coin.
Go to the signature campaign's thread (The specific thread linked on the overview thread), then follow their instructions, they usually vary, but most of them require you to give them your current post count and Bitcoin address. Also, different sig codes exist for different ranks, so make sure you pay attention to that.
I wouldn't buy an account for signature campaigns, it would take you an eternity to get a return on your investment, and you'd have to hope the account you bought is not a hacked account that eventually gets recovered. Buying an account for reselling purposes would be a lot more feasible, though the risk of buying an account that has a loan out or is hacked will still be there.