I believe that without signature campaign you probably could earn through the freelance work or offering goods and services, check the services section.
That is the only way that can earn you good amounts on this forum besides signature campaign... To offer your services and wait to get hired by someone so that when you do his work he pays you with bitcoins... Or you may also sell some stuff like physical or digital goods..
Yes apart from signature campaign I think better ways to earn bitcoins is by buying and selling digital goods and you can also buy lower rank accounts, work on it and upgrade them and sell at higher price.