1) Making a fixed campaign with 0.2 per month for 5 best quality posters, min requirement only 20 posts , so something like 0.01 per post.
2) Advertising in bitcointalk with banner ads, with only one slot for 1btc per month.
IMO signatures are better because you get better visibility.
It's not foolish for people to use the banner ads. Some people actually click those rather than those links on the signature campaigns but still, if you want fast advertising to be in every part of the forum then signature is always better. Also those signature campaigns that pays you in your account in their site gains more user.