This is tricky question but part from work here signature and avatar you can make 0.06 btc max
With something else to offer you can make more to be campaign manager or something else offer service in design here bb code ann treads banners
Signatures is a way but there is no guarantee your campaigns last. That's why it's better to start with your own kind of business on bitcointalk.org. Sell writing skills, or your time and you will see more and more people will buy your service. Eventually it will be well over 0.1 BTC per week.