Earn 0.5 BTC a month? I don't think that you can 0.5 BTC in signature if your rank is Sr. Member below maybe Hero member above,
I suggest to you to try trading you can earn beyond 0.5 BTC if your capital is great.
Depend on what rank you hold and which campaign you are in, and it also depends on maximum number of posts campaign allows you in week, bit x allows 150 posts per week, and if you are hero then you can easily make 0.48 per month.